[clang] [clang][python] Add CLANG_DISABLE_RUN_PYTHON_TESTS CMake option to disable clang python bindings tests (PR #111367)

[Alex Bradbury via cfe-commits]

asb wrote:

> > Though now I write this, I'm thinking it would make more sense to set RUN_PYTHON_TESTS to FALSE if CMAKE_CROSSCOMPILING is set. What do you think?
> 
> Yes, I like this direction much more. Probably you should also print a message during configuration saying that those tests are excluded because of cross setup.

Thanks for the review and feedback, definitely a better solution. I've posted it as a separate PR rather than reworking this one because it's a fundamentally different approach and editing this one would be confusing when coming back later. https://github.com/llvm/llvm-project/pull/111657

> Do you know what the state of support for cross environments is in general? If they are generally well-maintained, we're more incentivized to do a proper support for them in Python bindings tests.

Now I've landed https://github.com/llvm/llvm-project/pull/111373 a cross-build and then check-all actually works surprisingly well. I'm not sure to what degree I'd consider it officially supported, but I'm working to clean it up a bit as I think there's scope for taking more advantage of this setup for local development, litmus testing for releases, and at least some CI (on the staging buildmaster if not the main one).

https://github.com/llvm/llvm-project/pull/111367