[clang] Support C++20 Modules in clang-repl (PR #79261)

[Vassil Vassilev via cfe-commits]

vgvassilev wrote:

We pass the CompilerInstance's notion of the target triple this commit explains it: https://github.com/llvm/llvm-project/commit/49f9532165f0cc0485a7da84662ebf63d155652c

@nathanchance, can `clang-repl` be run on your setup? If the Jit is happy about the target triple and we can jit code that'd probably mean that the modules infrastructure gets confused about the target triple and build a C++ module for the wrong configuration.

https://github.com/llvm/llvm-project/pull/79261