ARM interrupt attribute warning doesn't have its own flag

[llvmbot]

Bugzilla Link	35528
Version	trunk
OS	All
Reporter	LLVM Bugzilla Contributor

Extended Description

https://reviews.llvm.org/D28820

Not sure what to call it. How about -Warm-interrupt-safety?

[llvmbot]

patch to fix this in: https://reviews.llvm.org/D74812