[PATCH][libstc++v3]Add new dg-require-thread-fence directive.

[PATCH][libstc++v3]Add new dg-require-thread-fence directive.

libstdc++-v3/

2015-04-22  Renlin Li  <renlin.li@arm.com>

	* testsuite/lib/dg-options.exp (dg-require-thread-fence): New.
	* testsuite/lib/libstdc++.exp (check_v3_target_thread_fence): New.
	* testsuite/29_atomics/atomic_flag/clear/1.cc: Use it.
	* testsuite/29_atomics/atomic_flag/test_and_set/explicit.cc: Likewise.
	* testsuite/29_atomics/atomic_flag/test_and_set/implicit.cc: Likewise.

From-SVN: r222324