[clang] [clang][Sema] Emit warnings about incorrect AVR interrupt/signal handlers (PR #125997)

[Jianjian Guan via cfe-commits]

================
@@ -351,8 +351,8 @@ def warn_arm_interrupt_vfp_clobber : Warning<
 def err_arm_interrupt_called : Error<
   "interrupt service routine cannot be called directly">;
 def warn_interrupt_attribute_invalid : Warning<
----------------
jacquesguan wrote:

Maybe change this name since it also contains 'signal' now?

https://github.com/llvm/llvm-project/pull/125997