PR libstdc++/51798 continued

PR libstdc++/51798 continued
	* include/bits/shared_ptr_base.h
	(_Sp_counted_base<_S_atomic>::_M_add_ref_lock): Hoist initial load
	outside compare_exchange loop.
	* include/tr1/shared_ptr.h: Same.
	* include/parallel/compatibility.h (__compare_and_swap_32): Use strong
	version of compare_exchange.
	(__compare_and_swap_64): Same.
	* include/profile/impl/profiler_state.h (__gnu_profile::__turn): Same.
	* libsupc++/guard.cc (__cxa_guard_acquire): Same.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@184171 138bc75d-0d04-0410-961f-82ee72b054a4