diff --git a/.github/workflows/ci_iwyu.yml b/.github/workflows/ci_iwyu.yml
index 0cc086cf..4c7d4f31 100644
--- a/.github/workflows/ci_iwyu.yml
+++ b/.github/workflows/ci_iwyu.yml
@@ -44,7 +44,6 @@ jobs:
       - name: Install Dependencies
         run: |
           install libomp-17-dev libclang-17-dev
-          sudo ln -s /usr/lib/llvm-17/lib/clang/17 /usr/lib/llvm-17/lib/clang/17.0.0
 
       - name: Install CMake
         uses: seqan/actions/setup-cmake@main
@@ -56,7 +55,7 @@ jobs:
           clang-17 -print-resource-dir
           mkdir iwyu
           cd iwyu
-          git clone https://github.com/include-what-you-use/include-what-you-use.git
+          git clone https://github.com/include-what-you-use/include-what-you-use.git --branch 0.21
           mkdir build
           cd build
           cmake ../include-what-you-use -G "Unix Makefiles" \
diff --git a/test/iwyu/mappings/gcc.symbols.imp b/test/iwyu/mappings/gcc.symbols.imp
index 8b9e0fb8..7ac91fdc 100644
--- a/test/iwyu/mappings/gcc.symbols.imp
+++ b/test/iwyu/mappings/gcc.symbols.imp
@@ -18,56 +18,38 @@
 [
   { symbol: [ "aiocb", private, "<aio.h>", private ] },
   { symbol: [ "blkcnt_t", private, "<sys/types.h>", private ] },
-  { symbol: [ "blkcnt_t", private, "<sys/stat.h>", private ] },
   { symbol: [ "blksize_t", private, "<sys/types.h>", private ] },
-  { symbol: [ "blksize_t", private, "<sys/stat.h>", private ] },
   { symbol: [ "cc_t", private, "<termios.h>", private ] },
-  { symbol: [ "clock_t", private, "<sys/types.h>", private ] },
-  { symbol: [ "clock_t", private, "<sys/time.h>", private ] },
   { symbol: [ "clock_t", private, "<time.h>", private ] },
+  { symbol: [ "clock_t", private, "<sys/types.h>", private ] },
   { symbol: [ "clockid_t", private, "<sys/types.h>", private ] },
-  { symbol: [ "clockid_t", private, "<time.h>", private ] },
   { symbol: [ "daddr_t", private, "<sys/types.h>", private ] },
-  { symbol: [ "daddr_t", private, "<rpc/types.h>", private ] },
   { symbol: [ "dev_t", private, "<sys/types.h>", private ] },
-  { symbol: [ "dev_t", private, "<sys/stat.h>", private ] },
   { symbol: [ "div_t", private, "<stdlib.h>", private ] },
   { symbol: [ "double_t", private, "<math.h>", private ] },
   { symbol: [ "error_t", private, "<errno.h>", private ] },
   { symbol: [ "error_t", private, "<argp.h>", private ] },
   { symbol: [ "error_t", private, "<argz.h>", private ] },
   { symbol: [ "fd_set", private, "<sys/select.h>", private ] },
-  { symbol: [ "fd_set", private, "<sys/time.h>", private ] },
   { symbol: [ "fenv_t", private, "<fenv.h>", private ] },
   { symbol: [ "fexcept_t", private, "<fenv.h>", private ] },
   { symbol: [ "FILE", private, "<stdio.h>", private ] },
   { symbol: [ "FILE", private, "<wchar.h>", private ] },
   { symbol: [ "float_t", private, "<math.h>", private ] },
   { symbol: [ "fsblkcnt_t", private, "<sys/types.h>", private ] },
-  { symbol: [ "fsblkcnt_t", private, "<sys/statvfs.h>", private ] },
   { symbol: [ "fsfilcnt_t", private, "<sys/types.h>", private ] },
-  { symbol: [ "fsfilcnt_t", private, "<sys/statvfs.h>", private ] },
   { symbol: [ "getopt", private, "<unistd.h>", private ] },
   { symbol: [ "gid_t", private, "<sys/types.h>", private ] },
-  { symbol: [ "gid_t", private, "<grp.h>", private ] },
-  { symbol: [ "gid_t", private, "<pwd.h>", private ] },
-  { symbol: [ "gid_t", private, "<signal.h>", private ] },
-  { symbol: [ "gid_t", private, "<stropts.h>", private ] },
-  { symbol: [ "gid_t", private, "<sys/ipc.h>", private ] },
-  { symbol: [ "gid_t", private, "<sys/stat.h>", private ] },
   { symbol: [ "gid_t", private, "<unistd.h>", private ] },
   { symbol: [ "htonl", private, "<arpa/inet.h>", private ] },
   { symbol: [ "htons", private, "<arpa/inet.h>", private ] },
   { symbol: [ "id_t", private, "<sys/types.h>", private ] },
-  { symbol: [ "id_t", private, "<sys/resource.h>", private ] },
   { symbol: [ "imaxdiv_t", private, "<inttypes.h>", private ] },
   { symbol: [ "intmax_t", private, "<stdint.h>", private ] },
   { symbol: [ "uintmax_t", private, "<stdint.h>", private ] },
   { symbol: [ "ino64_t", private, "<sys/types.h>", private ] },
   { symbol: [ "ino64_t", private, "<dirent.h>", private ] },
   { symbol: [ "ino_t", private, "<sys/types.h>", private ] },
-  { symbol: [ "ino_t", private, "<dirent.h>", private ] },
-  { symbol: [ "ino_t", private, "<sys/stat.h>", private ] },
   { symbol: [ "int8_t", private, "<stdint.h>", private ] },
   { symbol: [ "int16_t", private, "<stdint.h>", private ] },
   { symbol: [ "int32_t", private, "<stdint.h>", private ] },
@@ -79,155 +61,71 @@
   { symbol: [ "intptr_t", private, "<stdint.h>", private ] },
   { symbol: [ "uintptr_t", private, "<stdint.h>", private ] },
   { symbol: [ "iovec", private, "<sys/uio.h>", private ] },
-  { symbol: [ "iovec", private, "<sys/socket.h>", private ] },
   { symbol: [ "itimerspec", private, "<time.h>", private ] },
-  { symbol: [ "itimerspec", private, "<sys/timerfd.h>", private ] },
   { symbol: [ "key_t", private, "<sys/types.h>", private ] },
-  { symbol: [ "key_t", private, "<sys/ipc.h>", private ] },
   { symbol: [ "lconv", private, "<locale.h>", private ] },
   { symbol: [ "ldiv_t", private, "<stdlib.h>", private ] },
   { symbol: [ "lldiv_t", private, "<stdlib.h>", private ] },
   { symbol: [ "max_align_t", private, "<stddef.h>", private ] },
   { symbol: [ "mode_t", private, "<sys/types.h>", private ] },
-  { symbol: [ "mode_t", private, "<fcntl.h>", private ] },
-  { symbol: [ "mode_t", private, "<ndbm.h>", private ] },
-  { symbol: [ "mode_t", private, "<spawn.h>", private ] },
-  { symbol: [ "mode_t", private, "<sys/ipc.h>", private ] },
-  { symbol: [ "mode_t", private, "<sys/mman.h>", private ] },
-  { symbol: [ "mode_t", private, "<sys/stat.h>", private ] },
   { symbol: [ "nlink_t", private, "<sys/types.h>", private ] },
-  { symbol: [ "nlink_t", private, "<sys/stat.h>", private ] },
   { symbol: [ "ntohl", private, "<arpa/inet.h>", private ] },
   { symbol: [ "ntohs", private, "<arpa/inet.h>", private ] },
   { symbol: [ "off64_t", private, "<sys/types.h>", private ] },
   { symbol: [ "off64_t", private, "<unistd.h>", private ] },
   { symbol: [ "off_t", private, "<sys/types.h>", private ] },
-  { symbol: [ "off_t", private, "<aio.h>", private ] },
-  { symbol: [ "off_t", private, "<fcntl.h>", private ] },
-  { symbol: [ "off_t", private, "<stdio.h>", private ] },
-  { symbol: [ "off_t", private, "<sys/mman.h>", private ] },
-  { symbol: [ "off_t", private, "<sys/stat.h>", private ] },
   { symbol: [ "off_t", private, "<unistd.h>", private ] },
   { symbol: [ "optarg", private, "<unistd.h>", private ] },
   { symbol: [ "opterr", private, "<unistd.h>", private ] },
   { symbol: [ "optind", private, "<unistd.h>", private ] },
   { symbol: [ "optopt", private, "<unistd.h>", private ] },
   { symbol: [ "pid_t", private, "<sys/types.h>", private ] },
-  { symbol: [ "pid_t", private, "<fcntl.h>", private ] },
-  { symbol: [ "pid_t", private, "<sched.h>", private ] },
-  { symbol: [ "pid_t", private, "<signal.h>", private ] },
-  { symbol: [ "pid_t", private, "<spawn.h>", private ] },
-  { symbol: [ "pid_t", private, "<sys/msg.h>", private ] },
-  { symbol: [ "pid_t", private, "<sys/sem.h>", private ] },
-  { symbol: [ "pid_t", private, "<sys/shm.h>", private ] },
-  { symbol: [ "pid_t", private, "<sys/wait.h>", private ] },
-  { symbol: [ "pid_t", private, "<termios.h>", private ] },
-  { symbol: [ "pid_t", private, "<time.h>", private ] },
   { symbol: [ "pid_t", private, "<unistd.h>", private ] },
-  { symbol: [ "pid_t", private, "<utmpx.h>", private ] },
   { symbol: [ "ptrdiff_t", private, "<stddef.h>", private ] },
   { symbol: [ "regex_t", private, "<regex.h>", private ] },
   { symbol: [ "regmatch_t", private, "<regex.h>", private ] },
   { symbol: [ "regoff_t", private, "<regex.h>", private ] },
   { symbol: [ "sigevent", private, "<signal.h>", private ] },
-  { symbol: [ "sigevent", private, "<aio.h>", private ] },
-  { symbol: [ "sigevent", private, "<mqueue.h>", private ] },
-  { symbol: [ "sigevent", private, "<time.h>", private ] },
   { symbol: [ "siginfo_t", private, "<signal.h>", private ] },
-  { symbol: [ "siginfo_t", private, "<sys/wait.h>", private ] },
   { symbol: [ "sigset_t", private, "<signal.h>", private ] },
-  { symbol: [ "sigset_t", private, "<spawn.h>", private ] },
-  { symbol: [ "sigset_t", private, "<sys/select.h>", private ] },
   { symbol: [ "sigval", private, "<signal.h>", private ] },
   { symbol: [ "sockaddr", private, "<sys/socket.h>", private ] },
   { symbol: [ "socklen_t", private, "<sys/socket.h>", private ] },
-  { symbol: [ "socklen_t", private, "<netdb.h>", private ] },
   { symbol: [ "ssize_t", private, "<sys/types.h>", private ] },
-  { symbol: [ "ssize_t", private, "<aio.h>", private ] },
-  { symbol: [ "ssize_t", private, "<monetary.h>", private ] },
-  { symbol: [ "ssize_t", private, "<mqueue.h>", private ] },
-  { symbol: [ "ssize_t", private, "<stdio.h>", private ] },
-  { symbol: [ "ssize_t", private, "<sys/msg.h>", private ] },
-  { symbol: [ "ssize_t", private, "<sys/socket.h>", private ] },
-  { symbol: [ "ssize_t", private, "<sys/uio.h>", private ] },
   { symbol: [ "ssize_t", private, "<unistd.h>", private ] },
   { symbol: [ "stat", private, "<sys/stat.h>", private ] },
-  { symbol: [ "stat", private, "<ftw.h>", private ] },
   { symbol: [ "suseconds_t", private, "<sys/types.h>", private ] },
-  { symbol: [ "suseconds_t", private, "<sys/select.h>", private ] },
-  { symbol: [ "suseconds_t", private, "<sys/time.h>", private ] },
   { symbol: [ "time_t", private, "<time.h>", private ] },
-  { symbol: [ "time_t", private, "<sched.h>", private ] },
-  { symbol: [ "time_t", private, "<sys/msg.h>", private ] },
-  { symbol: [ "time_t", private, "<sys/select.h>", private ] },
-  { symbol: [ "time_t", private, "<sys/sem.h>", private ] },
-  { symbol: [ "time_t", private, "<sys/shm.h>", private ] },
-  { symbol: [ "time_t", private, "<sys/stat.h>", private ] },
-  { symbol: [ "time_t", private, "<sys/time.h>", private ] },
   { symbol: [ "time_t", private, "<sys/types.h>", private ] },
-  { symbol: [ "time_t", private, "<utime.h>", private ] },
   { symbol: [ "timer_t", private, "<sys/types.h>", private ] },
-  { symbol: [ "timer_t", private, "<time.h>", private ] },
   { symbol: [ "timespec", private, "<time.h>", private ] },
-  { symbol: [ "timespec", private, "<aio.h>", private ] },
-  { symbol: [ "timespec", private, "<mqueue.h>", private ] },
-  { symbol: [ "timespec", private, "<sched.h>", private ] },
   { symbol: [ "timespec", private, "<signal.h>", private ] },
-  { symbol: [ "timespec", private, "<sys/select.h>", private ] },
-  { symbol: [ "timespec", private, "<sys/stat.h>", private ] },
   { symbol: [ "timeval", private, "<sys/time.h>", private ] },
-  { symbol: [ "timeval", private, "<sys/resource.h>", private ] },
-  { symbol: [ "timeval", private, "<sys/select.h>", private ] },
-  { symbol: [ "timeval", private, "<utmpx.h>", private ] },
   { symbol: [ "tm", private, "<time.h>", private ] },
   { symbol: [ "u_char", private, "<sys/types.h>", private ] },
-  { symbol: [ "u_char", private, "<rpc/types.h>", private ] },
   { symbol: [ "uid_t", private, "<sys/types.h>", private ] },
-  { symbol: [ "uid_t", private, "<pwd.h>", private ] },
-  { symbol: [ "uid_t", private, "<signal.h>", private ] },
-  { symbol: [ "uid_t", private, "<stropts.h>", private ] },
-  { symbol: [ "uid_t", private, "<sys/ipc.h>", private ] },
-  { symbol: [ "uid_t", private, "<sys/stat.h>", private ] },
   { symbol: [ "uid_t", private, "<unistd.h>", private ] },
   { symbol: [ "useconds_t", private, "<sys/types.h>", private ] },
   { symbol: [ "useconds_t", private, "<unistd.h>", private ] },
   { symbol: [ "wchar_t", private, "<stddef.h>", private ] },
   { symbol: [ "wchar_t", private, "<stdlib.h>", private ] },
   { symbol: [ "size_t", private, "<stddef.h>", private ] },
-  { symbol: [ "size_t", private, "<aio.h>", private ] },
-  { symbol: [ "size_t", private, "<glob.h>", private ] },
-  { symbol: [ "size_t", private, "<grp.h>", private ] },
-  { symbol: [ "size_t", private, "<iconv.h>", private ] },
-  { symbol: [ "size_t", private, "<monetary.h>", private ] },
-  { symbol: [ "size_t", private, "<mqueue.h>", private ] },
-  { symbol: [ "size_t", private, "<ndbm.h>", private ] },
-  { symbol: [ "size_t", private, "<pwd.h>", private ] },
-  { symbol: [ "size_t", private, "<regex.h>", private ] },
-  { symbol: [ "size_t", private, "<search.h>", private ] },
   { symbol: [ "size_t", private, "<signal.h>", private ] },
   { symbol: [ "size_t", private, "<stdio.h>", private ] },
   { symbol: [ "size_t", private, "<stdlib.h>", private ] },
   { symbol: [ "size_t", private, "<string.h>", private ] },
-  { symbol: [ "size_t", private, "<strings.h>", private ] },
-  { symbol: [ "size_t", private, "<sys/mman.h>", private ] },
-  { symbol: [ "size_t", private, "<sys/msg.h>", private ] },
-  { symbol: [ "size_t", private, "<sys/sem.h>", private ] },
-  { symbol: [ "size_t", private, "<sys/shm.h>", private ] },
-  { symbol: [ "size_t", private, "<sys/socket.h>", private ] },
   { symbol: [ "size_t", private, "<sys/types.h>", private ] },
-  { symbol: [ "size_t", private, "<sys/uio.h>", private ] },
   { symbol: [ "size_t", private, "<time.h>", private ] },
   { symbol: [ "size_t", private, "<uchar.h>", private ] },
   { symbol: [ "size_t", private, "<unistd.h>", private ] },
   { symbol: [ "size_t", private, "<wchar.h>", private ] },
-  { symbol: [ "size_t", private, "<wordexp.h>", private ] },
   # Macros that can be defined in more than one file, don't have the
   # same __foo_defined guard that other types do, so the grep above
   # doesn't discover them.  Until I figure out a better way, I just
   # add them in by hand as I discover them.
   { symbol: [ "EOF", private, "<stdio.h>", private ] },
-  { symbol: [ "EOF", private, "<libio.h>", private ] },
   { symbol: [ "FILE", private, "<stdio.h>", private ] },
+  { symbol: [ "IBSHIFT", private, "<asm/termbits.h>", private ] },
   { symbol: [ "MAP_POPULATE", private, "<sys/mman.h>", private ] },
   { symbol: [ "MAP_POPULATE", private, "<linux/mman.h>", private ] },
   { symbol: [ "MAP_STACK", private, "<sys/mman.h>", private ] },
@@ -236,7 +134,6 @@
   { symbol: [ "MAXHOSTNAMELEN", private, "<protocols/timed.h>", private ] },
   { symbol: [ "SIGABRT", private, "<signal.h>", private ] },
   { symbol: [ "SIGCHLD", private, "<signal.h>", private ] },
-  { symbol: [ "SIGCHLD", private, "<linux/signal.h>", private ] },
   { symbol: [ "va_list", private, "<stdarg.h>", private ] },
   { symbol: [ "va_list", private, "<stdio.h>", private ] },
   { symbol: [ "va_list", private, "<wchar.h>", private ] },
@@ -262,6 +159,7 @@
   { symbol: [ "NULL", private, "<time.h>", private ] },
   { symbol: [ "NULL", private, "<unistd.h>", private ] },
   { symbol: [ "NULL", private, "<wchar.h>", private ] },
+  { symbol: [ "offsetof", private, "<stddef.h>", private ] },
 
   # GCC defines std::declval in <type_traits>, but the canonical location is <utility>
   { symbol: [ "std::declval", private, "<utility>", public ] },