[clang] [modulemap] Add -fno-implicit-module-map-file= to exclude from implicit discovery (PR #208191)

[Tor Arne Vestbø via cfe-commits]

torarnv wrote:

> > Oh, if you import `Foundation` you'll likely need `--language objective-c++`, otherwise we can take a look with the same input framework you're using.
> 
> Aah, much better! Now I see a single error, that looks to be a valid issue in the module map. Thanks!

Actually, this failure is why I originally went with a manual `clang` invocation in https://codereview.qt-project.org/c/qt/qtbase/+/674683/31/tests/auto/cmake/test_clang_module_maps/CMakeLists.txt

The `modules-verifier` seems to create a separate `Test` module that just slurps in all the headers in the given framework, even if the framework already has a hand-written module map. That approach doesn't work for Qt that has lots of private headers that should be excluded: https://gist.github.com/torarnv/80cdd6d9a12006349392ed09fd90fee5

Looks like my manual test is passing all the same `-W` flags though, so we should be good testing-wise for now AFAICT.

https://github.com/llvm/llvm-project/pull/208191