CMake: fix Emscripten build. Instead of setting things in CMake itself, the toolchain file should be provided via `-DCMAKE_TOOLCHAIN_FILE`.
CMake: fix Emscripten build.
Instead of setting things in CMake itself, the toolchain file should be provided via `-DCMAKE_TOOLCHAIN_FILE`.

spirit-code/spirit,spirit-code/spirit,spirit-code/spirit,spirit-code/spirit,spirit-code/spirit,spirit-code/spirit