* Note, this patch supersedes my previous atomic wait and semaphore
patches.

Add support for -
        atomic wait/notify_one/notify_all
        counting_semaphore
        binary_semaphore
        latch

        * include/Makefile.am (bits_headers): Add new header.
        * include/Makefile.in: Regenerate.
        * include/bits/atomic_base.h (__atomic_base<_Itp>:wait): Define.
        (__atomic_base<_Itp>::notify_one): Likewise.
        (__atomic_base<_Itp>::notify_all): Likewise.
        (__atomic_base<_Ptp*>::wait): Likewise.
        (__atomic_base<_Ptp*>::notify_one): Likewise.
        (__atomic_base<_Ptp*>::notify_all): Likewise.
        (__atomic_impl::wait): Likewise.
        (__atomic_impl::notify_one): Likewise.
        (__atomic_impl::notify_all): Likewise.
        (__atomic_float<_Fp>::wait): Likewise.
        (__atomic_float<_Fp>::notify_one): Likewise.
        (__atomic_float<_Fp>::notify_all): Likewise.
        (__atomic_ref<_Tp>::wait): Likewise.
        (__atomic_ref<_Tp>::notify_one): Likewise.
        (__atomic_ref<_Tp>::notify_all): Likewise.
        (atomic_wait<_Tp>): Likewise.
        (atomic_wait_explicit<_Tp>): Likewise.
        (atomic_notify_one<_Tp>): Likewise.
        (atomic_notify_all<_Tp>): Likewise.
        * include/bits/atomic_wait.h: New file.
        * include/bits/atomic_timed_wait.h: New file.
        * include/bits/semaphore_base.h: New file.
        * include/std/atomic (atomic<bool>::wait): Define.
        (atomic<bool>::wait_one): Likewise.
        (atomic<bool>::wait_all): Likewise.
        (atomic<_Tp>::wait): Likewise.
        (atomic<_Tp>::wait_one): Likewise.
        (atomic<_Tp>::wait_all): Likewise.
        (atomic<_Tp*>::wait): Likewise.
        (atomic<_Tp*>::wait_one): Likewise.
        (atomic<_Tp*>::wait_all): Likewise.
        * include/std/latch: New file.
        * include/std/semaphore: New file.
        * include/std/version: Add __cpp_lib_semaphore and
        __cpp_lib_latch defines.
        * testsuite/29_atomic/atomic/wait_notify/atomic_refs.cc: New test.
        * testsuite/29_atomic/atomic/wait_notify/bool.cc: Likewise.
        * testsuite/29_atomic/atomic/wait_notify/integrals.cc: Likewise.
        * testsuite/29_atomic/atomic/wait_notify/floats.cc: Likewise.
        * testsuite/29_atomic/atomic/wait_notify/pointers.cc: Likewise.
        * testsuite/29_atomic/atomic/wait_notify/generic.h: New File.
        * testsuite/30_thread/semaphore/1.cc: New test.
        * testsuite/30_thread/semaphore/2.cc: Likewise.
        * testsuite/30_thread/semaphore/try_acquire.cc: Likewise.
        * testsuite/30_thread/semaphore/try_acquire_for.cc: Likewise.
        * testsuite/30_thread/semaphore/try_acquire_futex.cc: Likewise.
        * testsuite/30_thread/semaphore/try_acquire_posix.cc: Likewise.
        * testsuite/30_thread/semaphore/try_acquire_until.cc: Likewise.
        * testsuite/30_thread/latch/1.cc: New test.
        * testsuite/30_thread/latch/2.cc: New test.
        * testsuite/30_thread/latch/3.cc: New test