* sysdeps/posix/waitid.c (do_waitid) [DO_WAITID]: Define function
under this macro name instead.
[NO_DO_WAITID]: Don't define it at all.
(do_waitid) [WNOWAIT, WEXITED]: If these POSIX.1 waitid flag bits are
defined, then return ENOTSUP for combinations of selection bits other
than WEXITED and WEXITED|WSTOPPED, which this version cannot support.
* posix/tst-waitid.c: New file.
* posix/Makefile (tests): Add it.