This change was upstreamed in e5d853bbe9b05d6a00d98ad236f01937303e40c4
in GCC, but this file was slightly different in GCC 15, so we're
patching it manually.

diff --git a/libatomic/aclocal.m4 b/libatomic/aclocal.m4
index 80e24219d7d..581fedcfe13 100644
--- a/libatomic/aclocal.m4
+++ b/libatomic/aclocal.m4
@@ -1189,6 +1189,7 @@ AC_SUBST([am__untar])

 m4_include([../config/acx.m4])
 m4_include([../config/depstand.m4])
+m4_include([../config/gthr.m4])
 m4_include([../config/lead-dot.m4])
 m4_include([../config/lthostflags.m4])
 m4_include([../config/multi.m4])