ci: Update LLVM/Clang to 16.0 in nightly CI jobs on Windows
Also enable C++ modules tests with LLVM/Clang 16.0 on Windows. This works only with the GNU-like front-end and the Ninja generator.
Also enable C++ modules tests with LLVM/Clang 16.0 on Windows. This works only with the GNU-like front-end and the Ninja generator.