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

[Thorsten Beier via cfe-commits]

DerThorsten wrote:

> > > @AaronBallman, to be fair, clang is testing the wasm features in terms of output. So this is wiring up a bunch of tested features that will allow execution. Clang generally does not test execution but output, so we are not creating a precedent here since that PR can be considered plumbing for downstream consumers.
> > 
> > 
> > If we don't have community test coverage, we'll regress that plumbing for downstream consumers. In general, we shouldn't claim we support something we don't test. However, if there is a downstream consumer that agrees to be actively responsible for repairing breakages, we sometimes allow it (e.g., https://discourse.llvm.org/t/rfc-building-llvm-for-webassembly/79073)
> 
> I am not sure if we have the same definition for "claim". FWIW I am not saying we should put any of this on the website or elsewhere. We have a downstream consumer which intergrates the emscripten version of wasm [here](https://github.com/emscripten-forge/recipes/tree/main/recipes/recipes_emscripten/llvm). @DerThorsten is my go-to person when it comes to emscripten and llvm. I believe they are quite sensitive about breakages. In any case we will develop tests in the CppInterOp project, too.

For emscripten-forge recipes of xeus-cpp /clang  you can break whatever you want.
I am sure there are no deployments  / users yet

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