[gcc r13-5691] libstdc++: Mark pieces of gnu-linux/os_support.h linux-specific

[Jonathan Wakely <redi@gcc.gnu.org>]

https://gcc.gnu.org/g:f0065f207cf19cd960b33d961472c6d69514336f

commit r13-5691-gf0065f207cf19cd960b33d961472c6d69514336f
Author: Samuel Thibault <samuel.thibault@gnu.org>
Date:   Fri Oct 7 22:45:06 2022 +0200

    libstdc++: Mark pieces of gnu-linux/os_support.h linux-specific
    
    This is notably needed because in glibc 2.34, the move of pthread functions
    into libc.so happened for Linux only, not GNU/Hurd.
    
    The pthread_self() function can also always be used fine as it is on
    GNU/Hurd.
    
    libstdc++-v3/ChangeLog:
    
            * config/os/gnu-linux/os_defines.h [!__linux__]
            (_GLIBCXX_NATIVE_THREAD_ID, _GLIBCXX_GTHREAD_USE_WEAK): Do not define.
    
    Reviewed-by: Jonathan Wakely <jwakely@redhat.com>

Diff:
---
 libstdc++-v3/config/os/gnu-linux/os_defines.h | 22 +++++++++++++---------
 1 file changed, 13 insertions(+), 9 deletions(-)

diff --git a/libstdc++-v3/config/os/gnu-linux/os_defines.h b/libstdc++-v3/config/os/gnu-linux/os_defines.h
index 3064f8d908a..87317031fcd 100644
--- a/libstdc++-v3/config/os/gnu-linux/os_defines.h
+++ b/libstdc++-v3/config/os/gnu-linux/os_defines.h
@@ -60,22 +60,26 @@
 # define _GLIBCXX_HAVE_FLOAT128_MATH 1
 #endif
 
-#if __GLIBC_PREREQ(2, 27)
+#ifdef __linux__
+// The following libpthread properties only apply to Linux, not GNU/Hurd.
+
+# if __GLIBC_PREREQ(2, 27)
 // Since glibc 2.27 pthread_self() is usable without linking to libpthread.
-# define _GLIBCXX_NATIVE_THREAD_ID pthread_self()
-#else
+#  define _GLIBCXX_NATIVE_THREAD_ID pthread_self()
+# else
 // Before then it was in libc.so.6 but not libc.a, and always returns 0,
 // which breaks the invariant this_thread::get_id() != thread::id{}.
 // So only use it if we know the libpthread version is available.
 // Otherwise use (__gthread_t)1 as the ID of the main (and only) thread.
-# define _GLIBCXX_NATIVE_THREAD_ID \
-  (__gthread_active_p() ? __gthread_self() : (__gthread_t)1)
-#endif
+#  define _GLIBCXX_NATIVE_THREAD_ID \
+   (__gthread_active_p() ? __gthread_self() : (__gthread_t)1)
+# endif
 
-#if __GLIBC_PREREQ(2, 34)
+# if __GLIBC_PREREQ(2, 34)
 // Since glibc 2.34 all pthreads functions are usable without linking to
 // libpthread.
-# define _GLIBCXX_GTHREAD_USE_WEAK 0
-#endif
+#  define _GLIBCXX_GTHREAD_USE_WEAK 0
+# endif
+#endif // __linux__
 
 #endif