Check gnatmake version in gnat_version_compare

Tom de Vries pointed out that my earlier change to
gnat_version_compare made it actually test gcc's version -- not
gnat's.

This patch changes gnat_version_compare to examine gnatmake's version,
while preserving the nicer API.

Approved-By: Tom de Vries <tdevries@suse.de>
1 file changed