Use getopt_long() or getopt(), depending on the host

From: Jean-Christophe Dubois <jdubois@mc.com>.

We do not always have GNU getopt_long(), so when we don't, just use
getopt() and the short options.  We do this based on __GNU_LIBRARY__
being set, or not.  Originally from Jean-Christophe Dubois <jdubois@mc.com>.
Signed-off-by: Tom Rini <trini@kernel.crashing.org>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>