build: Add forgotten libGP.* dependency.
build: Add forgotten libGP.* dependency.

The library dependency on object files
was accidentally dropped. Add it back.

gfxprim/gfxprim,gfxprim/gfxprim,gfxprim/gfxprim,gfxprim/gfxprim,gfxprim/gfxprim