* src/c++11/futex.cc: New file.
	* include/bits/atomic_futex.h: New file.
	* include/std/future (__future_base::_State_baseV2): Use
	atomic_futex_unsigned instead of mutex+condvar.
	* src/c++11/futex.cc: Likewise.
	* include/Makefile.am: Add atomic_futex.h.
	* include/Makefile.in: Likewise.
	* src/c++11/Makefile.am: Add futex.cc.
	* src/c++11/Makefile.in: Likewise.

From-SVN: r219770