Consider merging all the clang projects into one

After !1174 (merged) is merged, we will have 3 (and maybe 4 if we count llvm-runtimes here) different projects that repack clang with tools that are necessary for building for a specific platform.

I propose that we merge these projects into a single one. I believe that would make it clearer to understand what is happening and the purpose of each project. Think clang-repacked or maybe we can rename the actual clang project to clang-base and the repacked clang to clang.

Other than semantics, this would be beneficial for reducing some code duplication as there is at least one tool (wasm32-compiler-rt) that is added to all of these projects separately.