CMake

Try adding emscripten to CI platforms #47

Job	Run time
build (Linux-x64, DAWN, SHARED, Debug)	39s
build (Linux-x64, DAWN, SHARED, Release)	42s
build (Linux-x64, WGPU, SHARED, Debug)	44s
build (Linux-x64, WGPU, SHARED, Release)	1m 0s
build (Linux-x64, WGPU, STATIC, Debug)	38s
build (Linux-x64, WGPU, STATIC, Release)	47s
build (Windows-MSVC-x64, DAWN, SHARED, Debug)	1m 1s
build (Windows-MSVC-x64, DAWN, SHARED, Release)	1m 35s
build (Windows-MSVC-x64, WGPU, SHARED, Debug)	1m 29s
build (Windows-MSVC-x64, WGPU, SHARED, Release)	1m 20s
build (Windows-MSVC-x64, WGPU, STATIC, Debug)	1m 31s
build (Windows-MSVC-x64, WGPU, STATIC, Release)	1m 36s
build (Windows-MSYS-x64, DAWN, SHARED, Debug)	1m 59s
build (Windows-MSYS-x64, DAWN, SHARED, Release)	2m 20s
build (Windows-MSYS-x64, WGPU, SHARED, Debug)	1m 59s
build (Windows-MSYS-x64, WGPU, SHARED, Release)	1m 36s
build (Windows-MSYS-x64, WGPU, STATIC, Debug)	2m 3s
build (Windows-MSYS-x64, WGPU, STATIC, Release)	2m 7s
build (MacOS-x64, DAWN, SHARED, Debug)	46s
build (MacOS-x64, DAWN, SHARED, Release)	47s
build (MacOS-x64, WGPU, SHARED, Debug)	56s
build (MacOS-x64, WGPU, SHARED, Release)	1m 15s
build (MacOS-x64, WGPU, STATIC, Debug)	1m 9s
build (MacOS-x64, WGPU, STATIC, Release)	1m 26s
build (MacOS-ARM, DAWN, SHARED, Debug)	33s
build (MacOS-ARM, DAWN, SHARED, Release)	31s
build (MacOS-ARM, WGPU, SHARED, Debug)	31s
build (MacOS-ARM, WGPU, SHARED, Release)	32s
build (MacOS-ARM, WGPU, STATIC, Debug)	32s
build (MacOS-ARM, WGPU, STATIC, Release)	35s
build (emscripten, ubuntu-latest, emcmake, 3.1.61)	37s
	35m 16s

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