N64: mupen64plus-gles2n64 not filling screen correctly

Issue reported here: https://retropie.org.uk/forum/topic/25671/mupen64plus-gles2n64-small-screen-in-the-down-left

This works fine on pre-mesa driver, where we use SDL to upscale the low res image to fullscreen, however no matter what options I try, I cannot get the same result on mesa, only a fullscreen high res image (which is viable, but not consistent with our other n64 emulators).

There are a bunch of ifdefs for VC on gles2n64. Eg: https://github.com/ricrpi/mupen64plus-video-gles2n64/blob/1f53773f9045f5f18b895fe41f166d272175d72f/src/OpenGL.cpp#L394 - the issue is probably somewhere around there. However, given that this is a fork of an abandoned plugin that has been modified to suit VC, I'm not so motivated to try and fix it. GLideN64 is the only in-development HLE plugin we use.

My suggestion is to only install gles2n64 (and ideally rice) for VC platforms.

Start with the linked gles2n64 src/OpenGL.cpp around line 394 and the RetroPie-Setup installation logic for N64 plugins. Reproduce the fullscreen behavior on Mesa and pre-Mesa drivers, then verify that gles2n64 (and, if appropriate, Rice) is installed only for VC platforms while other N64 setups remain unchanged.