[clang] [clang][ARM] Fix warning for VFP function calls from interrupts. (PR #91870)

[David Spickett via cfe-commits]

https://github.com/DavidSpickett commented:

I can't fully approve this, I leave that to other members of @llvm/pr-subscribers-arm .

2 overall comments:
* Calling a function marked interrupt from a function marked interrupt is still UB isn't it? Should there be another warning to cover that scenario as well?
* I see that gcc has a warning in `-Wattributes` for this, you should raise a bug there equivalent to the one llvm has, perhaps there even is one already.

https://github.com/llvm/llvm-project/pull/91870