[glibc] x86: Fix THREAD_GSCOPE_RESET_FLAG build on clang

[Adhemerval Zanella]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=e3394859eeee302edff09eb8ed0ec575aa8c5614

commit e3394859eeee302edff09eb8ed0ec575aa8c5614
Author: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Date:   Fri Oct 31 17:00:47 2025 -0300

    x86: Fix THREAD_GSCOPE_RESET_FLAG build on clang
    
    clang does not support __seg_fs in asm constraint.
    
    Reviewed-by: Uros Bizjak <ubizjak@gmail.com>

Diff:
---
 sysdeps/x86_64/nptl/tls.h | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/sysdeps/x86_64/nptl/tls.h b/sysdeps/x86_64/nptl/tls.h
index abfeb88054..9d53f05e65 100644
--- a/sysdeps/x86_64/nptl/tls.h
+++ b/sysdeps/x86_64/nptl/tls.h
@@ -198,10 +198,18 @@ _Static_assert (offsetof (tcbhead_t, __glibc_unused2) == 0x80,
 # define THREAD_GSCOPE_FLAG_UNUSED 0
 # define THREAD_GSCOPE_FLAG_USED   1
 # define THREAD_GSCOPE_FLAG_WAIT   2
+
+/* clang does not support __seg_fs in asm constraint.  */
+# ifdef __clang__
+#  define FS_ASM "%%fs:"
+# else
+#  define FS_ASM
+# endif
+
 # define THREAD_GSCOPE_RESET_FLAG() \
   do									      \
     { int __res;							      \
-      asm volatile ("xchgl %1, %0"					      \
+      asm volatile ("xchgl " FS_ASM "%1, %0"				      \
 		    : "=r" (__res)					      \
 		    : "m" (((struct pthread __seg_fs *)0)->header.gscope_flag), \
 		      "0" (THREAD_GSCOPE_FLAG_UNUSED));			      \