The POSIX waitid implementation is problematic in some ways:
- It emulates using waitpid, which default implementation calls
wait4 and wait4 returns ENOSYS as default.
- Also by using waitpid it does not allod support the WNOWAIT,
WEXITED, WSTOPPED, or WCONTINUED flag. With current POSIX
specification the flags are no longer marked as optional.
Also due BZ#23091 Hurd still uses the implementation, so it is moved
to as a Hurd arch-specific folder (with some minor cleanups).
Checked against a i686-gnu (run-built-tests=no)
