We should setup CI for the upcoming JS and wasm backends.
For the JS backend the following packages are needed from the CI environment (docker images):
- emscripten version 3.14 or better
- llvm 15
- (@TerrorJack: does the wasm backend need something else?)
Note that for now the testsuite doesn't fully pass. We expect it to pass before the merge (be it by disabling the most problematic tests when the JS backend is used).