an odd case where signals were not catched when debugging.
(main, empth_start): Using sa_handler with SA_SIGINFO is wrong.
Simply don't set SA_SIGINFO; the additional signal information is not
used anyway.
(OSXLFLAGS): Don't sweep undefined references under the carpet; link
with the right libraries instead.
(LINUXCFLAGS, LINUXPTHCFLAGS): Compile with symbols.