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

[Chris Copeland via cfe-commits]

chrisnc wrote:

Here is an example of the existing warning in action. https://godbolt.org/z/9e84EfeYP
It warns for calling a normal function, but the same function with an interrupt attribute does not warn. The `subs pc, lr, 4` in `bar_irq` goes back to `bl bar_irq`, creating an infinite loop, where the second `subs pc, lr, 4` from `bar_irq` is also unpredictable, because the processor mode will most likely be system/user.

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