[committed] libstdc++: Disable gthreads weak symbols for glibc 2.34 [PR103133]

[Jonathan Wakely]

Tested powerpc64le-linux, glibc 2.17 and 2.34, pushed to trunk.

We also want something like this for musl-based targets. And Florian has
suggested we should also disable the weak symbols for libstdc++.a, but
those need more work.

...

Since Glibc 2.34 all pthreads symbols are defined directly in libc not
libpthread, and since Glibc 2.32 we have used __libc_single_threaded to
avoid unnecessary locking in single-threaded programs. This means there
is no reason to avoid linking to libpthread now, and so no reason to use
weak symbols defined in gthr-posix.h for all the pthread_xxx functions.

libstdc++-v3/ChangeLog:

	PR libstdc++/100748
	PR libstdc++/103133
	* config/os/gnu-linux/os_defines.h (_GLIBCXX_GTHREAD_USE_WEAK):
	Define for glibc 2.34 and later.
---
 libstdc++-v3/config/os/gnu-linux/os_defines.h | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/libstdc++-v3/config/os/gnu-linux/os_defines.h b/libstdc++-v3/config/os/gnu-linux/os_defines.h
index d5bb2a1886e..3a053454195 100644
--- a/libstdc++-v3/config/os/gnu-linux/os_defines.h
+++ b/libstdc++-v3/config/os/gnu-linux/os_defines.h
@@ -61,4 +61,10 @@
   (__gthread_active_p() ? __gthread_self() : (__gthread_t)1)
 #endif
 
+#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
+
 #endif
-- 
2.31.1