* performance is much better on gles, but there are glitches - possibly tweaking some options could improve this
* rework logic to build twice on the rpi4. Shader code is initially patched, commenting out the problematic "invariant"
qualifier, and then later reverted for the opengl build.
* use addEmulator to add the gles version first, then use the existing code which calls addPort
* enable gl_nopartialtextureupdates by default on rpi (fixes slowdown on rpi4 in game, doesn't seem to harm rpi1-3/videocore)
* remove makefile patch and override instead with makefile vars for parameters - this should make it simpler for adding additional gles platforms
* apply makefile.inc changes on all systems (which allows passing through of cpu parameters)
* override makefile.inc OPTIM_RELEASE parameters so we use our default optimisations
