libstdc++: Add "futex" and "gthreads" effective-target keywords

This adds a new "futex" effective-target keyword that can be used to
selectively enable/disable tests based on _GLIBCXX_HAVE_LINUX_FUTEX,
instead of checking for that macro in the code.

It also adds "gthreads" as another one, to make the result of the
dg-require-gthreads directive usable in target selectors.

With these new keywords two tests that are currently only run for linux
can also be run for targets using gthr-single.h (e.g. AIX single-thread
multilib, and targets without a gthreads implementation).

libstdc++-v3/ChangeLog:

	* testsuite/18_support/96817.cc: Use new effective-target
	keywords to select supported targets more effectively.
	* testsuite/30_threads/call_once/66146.cc: Likewise.
	* testsuite/lib/libstdc++.exp (check_effective_target_futex):
	Define new proc.
	(check_effective_target_gthreads): Define new proc to replace
	dg-require-gthreads.

1 files changed, 6 insertions, 7 deletions

diff --git a/libstdc++-v3/testsuite/18_support/96817.cc b/libstdc++-v3/testsuite/18_support/96817.cc
index 4591a72..7f35f03 100644
--- a/libstdc++-v3/testsuite/18_support/96817.cc
+++ b/libstdc++-v3/testsuite/18_support/96817.cc
@@ -15,19 +15,18 @@
 // with this library; see the file COPYING3.  If not see
 // <http://www.gnu.org/licenses/>.
 
-// { dg-options "-pthread"  }
-// { dg-do run { target *-*-linux-gnu } }
-// { dg-require-effective-target pthread }
+// { dg-do run }
+// { dg-additional-options "-pthread" { target pthread } }
+
+// Static init cannot detect recursion for gthreads targets without futexes
+// (and the futex case can only detect it if __libc_single_threaded==true).
+// { dg-skip-if "unsupported" { gthreads && { ! futex } } }
 
 // PR libstdc++/96817
 
 #include <exception>
 #include <stdlib.h>
 
-#ifndef _GLIBCXX_HAVE_LINUX_FUTEX
-# error "This test requries futex support in the library"
-#endif
-
 int init()
 {
 #if __has_include(<sys/single_threaded.h>)