graphics/dri will not build with WITH_NEW_XORG on 9-STABLE after 9.2 was branched

[Kevin Oberman]

For some reason the Makefile attempts to use gcc to build dri on any
9-stable after 9.2 was branched. As the Makefile notes that base GCC prior
to 4.3 will not build.

Removing the test against $OSVERSION < 902503 will fix this and use clang
to build dri successfully.
-- 
R. Kevin Oberman, Network Engineer
E-mail: rkoberman at gmail.com