Fixes PP-shaders on !Mesa targets.

Seems mesa has a quirk where
define THING(x) (#x)
is the same as
define THING(x) (##x)

Didn't realize I messed it up since it just worked since I only tested on Mesa.
Merge pull request #827 from Sonicadvance1/fix-pp-config

Fixes PP-shaders on !Mesa targets.