Hack bsd.mesalib.mk for PC-BSD specifically. We want 10.3.0 to appear
on 10.0-REL and 10.1-REL, even though the 10.0-REL pkgs are building
the older 9.x mesa lib. This fixes issues with multiple repos being used,
and ensures even though the version number is the same, the correct
mesa version will be used for the base system.