glamor: Fix more fallback paths with non-GXcopy rop with GLES
Desktop GL can handle arbitrary rops here, GLES can't. The switch statement attempts to optimize some cases that GLES can still handle if we precompute the right pixel value, but we were then throwing that pixel value away and using gc->fgPixel anyway. Fix this, and now xts-render passes against glamor+gles.
glamor-fix-xts-for-gles in 4 minutes and 22 seconds (queued for 1 second)3 jobs for