libstdc++/5432
	* include/bits/ios_base.h: Use _Atomic_word for reference counts.
	* include/bits/localefwd.h: Likewise.
	Also use for std::locale::id::_S_highwater.
	* src/ios.cc (ios_base::xalloc): Use _Atomic_word.
	* src/locale.cc: Support new usage of _Atomic_word.
	(std::locale::classic): Guard entire function against reentry.
	* src/localename.cc: Support new usage of _Atomic_word.

From-SVN: r49195