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.

From-SVN: r184171