doc: modernize LDocs.

* ext/posix/posix.c (Pgetopt, Ppoll, Pfcntl, Pdirname, Pfnmatch)
(Pglob, Psymlink, Paccess, Pfadvise, Pumask, Putime, Pwaitpid)
(Psetlogmask): Modernize LDocs.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>