[glibc/maskray/clang] libc-symbols.h: Work around asm label issues with #pragma redefine_extname

[Fangrui Song <maskray@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=c71bbcb392fa59f32a45c3fdfc342620486e3041

commit c71bbcb392fa59f32a45c3fdfc342620486e3041
Author: Fangrui Song <maskray@google.com>
Date:   Sat Sep 25 18:50:02 2021 -0700

    libc-symbols.h: Work around asm label issues with #pragma redefine_extname
    
    Using asm labels can lead to `error: cannot apply asm label to function after its first use`
    in many places. `#pragma redefine_extname` has the same behavior with an asm label, but avoids the error.
    
    The symbol will not be properly renamed to a non-default version symbol.

Diff:
---
 include/libc-symbols.h | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/include/libc-symbols.h b/include/libc-symbols.h
index d41ecf4384..8a5a9ff0b3 100644
--- a/include/libc-symbols.h
+++ b/include/libc-symbols.h
@@ -534,9 +534,19 @@ for linking")
   __hidden_proto (name, , __GI_##name, ##attrs)
 #  define hidden_tls_proto(name, attrs...) \
   __hidden_proto (name, __thread, __GI_##name, ##attrs)
-#  define __hidden_proto(name, thread, internal, attrs...)	     \
+#  ifdef __clang__
+#   define __hidden_proto(name, thread, internal, attrs...)           \
+      extern thread __typeof (name) name \
+      __hidden_proto_hiddenattr (attrs); \
+      _Pragma (__redefine(name, internal))
+/* Note that this macro does not use __hidden_asmname, since it produces a string.  */
+#   define __redefine(name, internal) __stringize(redefine_extname name internal)
+#   define __stringize(X) #X
+#  else
+#   define __hidden_proto(name, thread, internal, attrs...)	     \
   extern thread __typeof (name) name __asm__ (__hidden_asmname (#internal)) \
   __hidden_proto_hiddenattr (attrs);
+#  endif
 #  define __hidden_asmname(name) \
   __hidden_asmname1 (__USER_LABEL_PREFIX__, name)
 #  define __hidden_asmname1(prefix, name) __hidden_asmname2(prefix, name)