autoconf: Enable missing-prototypes errors when available.

After the removal of the dri driver link test, this should help avoid
the original problem that it was designed to catch: The warning about
a missing prototype due to typoing a function name scrolling by in the
Mesa build spew, and you not noticing until you try to run an
application and it falls back to swrast.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
1 file changed