Tweak linux_glibc properties for musl builds in libcore

For convenience, builds against musl libc currently use the
linux_glibc properties because they are almost always linux-specific
and not glibc-specific.  In preparation for removing this hack,
tweak the linux_glibc properties by either moving them to host_linux,
which will apply to linux_glibc, linux_musl and linux_bionic, or
by setting appropriate musl or linux_musl properties.  Properties
that must not be repeated while musl uses linux_musl and also still
uses the linux_glibc properties are moved to glibc properties, which
don't apply to musl.  Whether these stay as glibc properties or get
moved back to linux_glibc later once the musl hack is removed is TBD.

Bug: 223257095
Test: m checkbuild
Test: m USE_HOST_MUSL=true host-native
Change-Id: I798f23b139c678040571009aa41322f8ad90f006

NativeCode.bp

@@ -135,15 +135,22 @@ cc_defaults {
     ],
 
     target: {
-        linux_glibc: {
-            cflags: [ // Sigh.
+        musl: {
+            cflags: [
+                // Sigh.
                 "-D_LARGEFILE64_SOURCE",
                 "-D_GNU_SOURCE",
                 "-DLINUX",
             ],
         },
         glibc: {
-            cflags: ["-D__GLIBC__"],
+            cflags: [
+                "-D__GLIBC__",
+                // Sigh.
+                "-D_LARGEFILE64_SOURCE",
+                "-D_GNU_SOURCE",
+                "-DLINUX",
+            ],
         },
         android: {
             shared_libs: [