This patch requires the patch for atomic<T>::wait/notify to be applied first.
This implementation is based on the libc++ implementation, but excludes the
alternative “central barrier” implementation for now as there is no standard
way to switch between the two.
* include/Makefile.am (std_headers): Add new header.
* include/Makefile.in: Regenerate.
* include/std/barrier: New file.
* testsuite/30_thread/barrier/1.cc: New test.
* testsuite/30_thread/barrier/2.cc: Likewise.
* testsuite/30_thread/barrier/arrive_and_drop.cc: Likewise.
* testsuite/30_thread/barrier/arrive_and_wait.cc: Likewise.
* testsuite/30_thread/barrier/arrive.cc: Likewise.
* testsuite/30_thread/barrier/completion.cc: Likewise.
* testsuite/30_thread/barrier/max.cc: Likewise.
