Drop memory barrier in _atomic_lock() implementation since the callers now
take care of this.

ok visa@, mpi@

Copy files from ../librthread in preparation for moving functionality
from libpthread to libc. No changes to the build yet, just making it
easier to review the substantive diffs.

ok beck@ kettenis@

Copy files from ../librthread in preparation for moving functionality
from libpthread to libc. No changes to the build yet, just making it
easier to review the substantive diffs.

ok beck@ kettenis@ tedu@

show more ...