The legacy `module.map` spelling of module map files was deprecated by llvm/llvm-project#75142 and clang expects to remove support for them in the future. Switch all tests to use the supported spelling.
Fixes rdar://128431478.
We use the just-built clang without any -target or -sdk flags. Keep things
simple and limit the test to macOS for now.
Fixes <rdar://problem/50586614>.