Add WASI (WebAssembly) cross compile support #157

Job	Run time
build-test (ubuntu-latest, gcc, amd64)	19m 45s
build-test (ubuntu-latest, gcc, c)	25m 25s
build-test (ubuntu-latest, clang, amd64)	20m 48s
build-test (ubuntu-latest, clang, c)	29m 52s
build-test (ubuntu-latest, clang, llvm)	30m 34s
build-test (macos-latest, clang, amd64)	47m 19s
build-test (macos-latest, clang, c)	49m 47s
build-test (macos-latest, clang, llvm)	57m 14s
build-test (windows-latest, gcc, amd64)	43m 3s
	5h 23m 47s

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