Set global C++ standard to C++17 for Emscripten #176

Job	Run time
Cancel Previous Runs	5s
Test Windows	4m 55s
Test Ubuntu	4m 1s
Test macOS	5m 46s
Build Release macOS	7m 48s
Build Release Web	3m 45s
Build Release Windows (OpenMP)	7m 47s
Build Release Windows	7m 40s
Build Release Windows (OpenMP) x64	8m 32s
Build Release Windows x64	8m 30s
Upload Release Assets	-1s
	58m 48s

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