Use atomics in guard.cc.

Use atomics in guard.cc.

This provides proper definitions for _GLIBCXX_READ_MEM_BARRIER and
_GLIBCXX_WRITE_MEM_BARRIER, rewrites the guards in terms of proper
atomic extensions and removes internal uses of
_GLIBCXX_READ_MEM_BARRIER and _GLIBCXX_WRITE_MEM_BARRIER and replaces
them with equivalent atomics.

2015-06-12  Ramana Radhakrishnan  <ramana.radhakrishnan@arm.com>

	PR target/66200
	PR c++/66192
	* * config/cpu/generic/atomic_word.h (_GLIBCXX_READ_MEM_BARRIER): Define
        (_GLIBCXX_WRITE_MEM_BARRIER): Likewise
        * include/bits/shared_ptr_base.h: Use ACQ_REL barrier.
        * include/ext/atomicity.h: Likewise.
        * include/tr1/shared_ptr.h: Likewise.
        * libsupc++/guard.cc (__test_and_acquire): Rewrite with atomics.
        Update comment.
        (__set_and_release): Likewise.
        * testsuite/20_util/shared_ptr/cons/43820_neg.cc (test01): Adjust for
	line numbers.
        * testsuite/20_util/shared_ptr/cons/void_neg.cc: Likewise.
        * testsuite/tr1/2_general_utilities/shared_ptr/cons/43820_neg.cc:
	Likewise.

From-SVN: r224411