Added GNU Makefile (#588) #155

Job	Run time
macOS	12m 16s
iOS	2m 29s
Android (SDL 2)	5m 4s
Windows (i686 (OGL))	6m 47s
Android (Native)	10m 46s
Windows (x86_64 (OGL + Shaders))	10m 2s
Windows (i686 (OGL + Shaders))	7m 12s
Windows (x86_64 (OGL))	10m 22s
Nintendo Switch	1m 57s
Flatpak (aarch64 SDL 2 (OGL + Shaders))	2m 19s
Linux (x86_64 SDL 2 (OGL))	1m 33s
Flatpak (x86_64 SDL 2 (OGL))	2m 5s
Flatpak (x86_64 SDL 2 (OGL + Shaders))	2m 1s
Flatpak (aarch64 SDL 2 (OGL))	2m 21s
Linux (i686 SDL 2 (OGL))	2m 13s
Linux (i686 SDL 2 (OGL + Shaders))	1m 59s
Linux (x86_64 SDL 2 (OGL + Shaders))	1m 38s
Linux (aarch64 SDL 2 (OGL + Shaders))	2m 7s
Linux (aarch64 SDL 2 (OGL))	1m 57s
	1h 27m 8s

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