[clang] [clang-repl] Support wasm execution (PR #86402)

[Anubhab Ghosh via cfe-commits]

argentite wrote:

> Unfortunately, this PR cannot be tested in the current testing infrastructure in llvm because it needs a browser to provide a proper execution environment.

Just to clarify, we don't need an actual full browser to test it. Nodejs should probably be sufficient for execution.

> That would make sense. I am not sure if we can set a post commit bot though. @argentite what do you think?

I think it is possible. If we use a buildbot, we currently only need to build llvm, clang and lld for WASM and targetting WASM. Other subprojects are not required for this PR and I am not even sure if they can be built to run in WASM.

Also most of the existing tests in the project (and maybe even the whole test infrastructure) probably won't work and/or does not make sense in WASM. So it would probably have to be running WASM specific tests.

https://github.com/llvm/llvm-project/pull/86402