toolchain/gdb: backport patch for macOS to fix invalid range

With the recent macOS update to Ventura, it looks like gdb could not be
compiled with clang16 and newer version, because it fails with:
./../gdbsupport/enum-flags.h:95:52: error: integer value -1 is outside the valid range of values [0, 15] for this enumeration type [-Wenum-constexpr-conversion]
    integer_for_size<sizeof (T), static_cast<bool>(T (-1) < T (0))>::type
                                                   ^
./../gdbsupport/enum-flags.h:95:52: error: integer value -1 is outside the valid range of values [0, 1] for this enumeration type [-Wenum-constexpr-conversion]
./../gdbsupport/enum-flags.h:95:52: error: integer value -1 is outside the valid range of values [0, 3] for this enumeration type [-Wenum-constexpr-conversion]
./../gdbsupport/enum-flags.h:95:52: error: integer value -1 is outside the valid range of values [0, 3] for this enumeration type [-Wenum-constexpr-conversion]
4 errors generated.

- Upstream bug:
https://sourceware.org/bugzilla/show_bug.cgi?id=30423

- Backported upstream commit:
https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=ae61525fcf456ab395d55c45492a106d1275873a

Fixes: openwrt/openwrt#15314

Signed-off-by: Josef Schlehofer <[email protected]>
Link: openwrt/openwrt#15315
Signed-off-by: Robert Marko <[email protected]>

toolchain/gdb/patches/0001-gdbsupport-ignore-Wenum-constexpr-conversion-in-enum.patch

@@ -0,0 +1,130 @@
+From e3b59e5461c81f03b608f24388af716c1983e2d0 Mon Sep 17 00:00:00 2001
+From: Simon Marchi <[email protected]>
+Date: Thu, 23 Feb 2023 17:35:40 +0000
+Subject: [PATCH] gdbsupport: ignore -Wenum-constexpr-conversion in
+ enum-flags.h
+
+When building with clang 16, we get:
+
+      CXX    gdb.o
+    In file included from /home/smarchi/src/binutils-gdb/gdb/gdb.c:19:
+    In file included from /home/smarchi/src/binutils-gdb/gdb/defs.h:65:
+    /home/smarchi/src/binutils-gdb/gdb/../gdbsupport/enum-flags.h:95:52: error: integer value -1 is outside the valid range of values [0, 15] for this enumeration type [-Wenum-constexpr-conversion]
+        integer_for_size<sizeof (T), static_cast<bool>(T (-1) < T (0))>::type
+                                                       ^
+
+The error message does not make it clear in the context of which enum
+flag this fails (i.e. what is T in this context), but it doesn't really
+matter, we have similar warning/errors for many of them, if we let the
+build go through.
+
+clang is right that the value -1 is invalid for the enum type we cast -1
+to.  However, we do need this expression in order to select an integer
+type with the appropriate signedness.  That is, with the same signedness
+as the underlying type of the enum.
+
+I first wondered if that was really needed, if we couldn't use
+std::underlying_type for that.  It turns out that the comment just above
+says:
+
+    /* Note that std::underlying_type<enum_type> is not what we want here,
+       since that returns unsigned int even when the enum decays to signed
+       int.  */
+
+I was surprised, because std::is_signed<std::underlying_type<enum_type>>
+returns the right thing.  So I tried replacing all this with
+std::underlying_type, see if that would work.  Doing so causes some
+build failures in unittests/enum-flags-selftests.c:
+
+      CXX    unittests/enum-flags-selftests.o
+    /home/smarchi/src/binutils-gdb/gdb/unittests/enum-flags-selftests.c:254:1: error: static assertion failed due to requirement 'gdb::is_same<selftests::enum_flags_tests::check_valid_expr254::archetype<enum_flags<s
+    elftests::enum_flags_tests::RE>, selftests::enum_flags_tests::RE, enum_flags<selftests::enum_flags_tests::RE2>, selftests::enum_flags_tests::RE2, enum_flags<selftests::enum_flags_tests::URE>, selftests::enum_fla
+    gs_tests::URE, int>, selftests::enum_flags_tests::check_valid_expr254::archetype<enum_flags<selftests::enum_flags_tests::RE>, selftests::enum_flags_tests::RE, enum_flags<selftests::enum_flags_tests::RE2>, selfte
+    sts::enum_flags_tests::RE2, enum_flags<selftests::enum_flags_tests::URE>, selftests::enum_flags_tests::URE, unsigned int>>::value == true':
+    CHECK_VALID (true,  int,  true ? EF () : EF2 ())
+    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+    /home/smarchi/src/binutils-gdb/gdb/unittests/enum-flags-selftests.c:91:3: note: expanded from macro 'CHECK_VALID'
+      CHECK_VALID_EXPR_6 (EF, RE, EF2, RE2, UEF, URE, VALID, EXPR_TYPE, EXPR)
+      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+    /home/smarchi/src/binutils-gdb/gdb/../gdbsupport/valid-expr.h:105:3: note: expanded from macro 'CHECK_VALID_EXPR_6'
+      CHECK_VALID_EXPR_INT (ESC_PARENS (typename T1, typename T2,           \
+      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+    /home/smarchi/src/binutils-gdb/gdb/../gdbsupport/valid-expr.h:66:3: note: expanded from macro 'CHECK_VALID_EXPR_INT'
+      static_assert (gdb::is_detected_exact<archetype<TYPES, EXPR_TYPE>,    \
+      ^              ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This is a bit hard to decode, but basically enumerations have the
+following funny property that they decay into a signed int, even if
+their implicit underlying type is unsigned.  This code:
+
+    enum A {};
+    enum B {};
+
+    int main() {
+      std::cout << std::is_signed<std::underlying_type<A>::type>::value
+                << std::endl;
+      std::cout << std::is_signed<std::underlying_type<B>::type>::value
+                << std::endl;
+      auto result = true ? A() : B();
+      std::cout << std::is_signed<decltype(result)>::value << std::endl;
+    }
+
+produces:
+
+    0
+    0
+    1
+
+So, the "CHECK_VALID" above checks that this property works for enum flags the
+same way as it would if you were using their underlying enum types.  And
+somehow, changing integer_for_size to use std::underlying_type breaks that.
+
+Since the current code does what we want, and I don't see any way of doing it
+differently, ignore -Wenum-constexpr-conversion around it.
+
+Change-Id: Ibc82ae7bbdb812102ae3f1dd099fc859dc6f3cc2
+---
+ gdbsupport/enum-flags.h | 3 +++
+ include/diagnostics.h   | 9 +++++++++
+ 2 files changed, 12 insertions(+)
+
+--- a/gdbsupport/enum-flags.h
++++ b/gdbsupport/enum-flags.h
+@@ -91,9 +91,12 @@ template<> struct integer_for_size<8, 1>
+ template<typename T>
+ struct enum_underlying_type
+ {
++  DIAGNOSTIC_PUSH
++  DIAGNOSTIC_IGNORE_ENUM_CONSTEXPR_CONVERSION
+   typedef typename
+     integer_for_size<sizeof (T), static_cast<bool>(T (-1) < T (0))>::type
+     type;
++  DIAGNOSTIC_POP
+ };
+
+ namespace enum_flags_detail
+--- a/include/diagnostics.h
++++ b/include/diagnostics.h
+@@ -66,6 +66,11 @@
+ # define DIAGNOSTIC_ERROR_SWITCH \
+   DIAGNOSTIC_ERROR ("-Wswitch")
+
++# if __has_warning ("-Wenum-constexpr-conversion")
++#  define DIAGNOSTIC_IGNORE_ENUM_CONSTEXPR_CONVERSION \
++   DIAGNOSTIC_IGNORE ("-Wenum-constexpr-conversion")
++# endif
++
+ #elif defined (__GNUC__) /* GCC */
+
+ # if __GNUC__ >= 7
+@@ -96,6 +101,10 @@
+ # define DIAGNOSTIC_IGNORE_DEPRECATED_DECLARATIONS
+ #endif
+
++#ifndef DIAGNOSTIC_IGNORE_ENUM_CONSTEXPR_CONVERSION
++# define DIAGNOSTIC_IGNORE_ENUM_CONSTEXPR_CONVERSION
++#endif
++
+ #ifndef DIAGNOSTIC_IGNORE_DEPRECATED_REGISTER
+ # define DIAGNOSTIC_IGNORE_DEPRECATED_REGISTER
+ #endif