Quake2 IRIX MesaFX/miniGL ports

Quake2 ports with MesaFX and (newly written) miniGL backends, both with dual TMU support.

-driver sources (SST1 and CVG support on IP32) https://github.com/sdz-mods/tdfx_irix
-glide2x IRIX port (SST1 on IP32) https://github.com/sdz-mods/glide_irix
-MesaFX IRIX port https://github.com/sdz-mods/MesaFX_irix

-Quake2 with miniGL backend https://github.com/sdz-mods/Quake2_irix_minigl
-Quake2 with MesaFX backend https://github.com/sdz-mods/Quake2_irix_mesafx

Current benchmark results (may improve in the future) @640×480, SST-1 (Voodoo1):

-Quake2 miniGL dual TMU: 17.6FPS
-Quake2 miniGL single TMU: 15.5FPS
-Quake2 MesaFX dual TMU: 17.0FPS
-Quake2 MesaFX single TMU: 14.8FPS