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

[Chris Copeland via cfe-commits]

chrisnc wrote:

@ahmedbougacha yes, I think it's correct that calling an `__attribute__((interrupt))` function is safe to do on M-profile because there is no difference in the return sequence; all it does is not assume that the stack is 8-byte aligned initially. Even then, this is only needed when not using the STKALIGN bit in CCR, which is on by default on most (all?) Cortex-M processors. This feature, along with the automatic volatile register saving, mean that `__attribute__((interrupt))` has almost no legitimate uses on M-profile.

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