[clang] [llvm] Enable running ClangReplInterpreterTests in an Emscripten environment (PR #150977)

[via llvm-commits]

mcbarton wrote:

@anutosh491 @vgvassilev I have double checked locally that just skipping hostsupportsjit allows the tests to still pass, and have pushed the changes to this PR. I have now applied the suggestion here https://github.com/llvm/llvm-project/pull/150977#discussion_r2241464970, as I believe it to be flawed (e.g. Emscripten/WebAssembly can have the wasm64-unknown-emscripten target as well as the wasm32-unknown-emscripten target). 

With regards to the InstantiateTemplate Value test comment here https://github.com/llvm/llvm-project/pull/150977#issuecomment-3134778392 the test crashes gtest, and I don't want this PR to become about fixing every test straight away. 

Finally with regards to the cmake change it is necessary. When you make the tests a main module, if there are any duplicate libraries being linked to then you get a duplicate symbol error when it tries to build the javascript. It still links to the llvmsupport library, but through clangInterpreter.

I think this PR is ready to go in now as a first step in having Emscripten tests for llvm clang-repl interpreter. Subsequent PRs can deal with getting everything to pass. 

https://github.com/llvm/llvm-project/pull/150977