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

[clang][ARM] Fix warning for using VFP from interrupts.

This warning has three issues:
- The interrupt attribute causes the function to return using an
exception
   return instruction. This warning allows calls from one function with
   the interrupt attribute to another, and the diagnostic text suggests
   that not having the attribute on the callee is a problem. Actually
   making such a call will lead to a double exception return, which is
   unpredictable according to the ARM architecture manual section
   B9.1.1, "Restrictions on exception return instructions". Even on
   machines where an exception return from user/system mode is
   tolerated, if the callee's interrupt type is anything other than a
   supervisor call or secure monitor call, it will also return to a
   different address than a normal function would. For example,
   returning from an "IRQ" handler will return to lr - 4, which will
   generally result in calling the same function again.
 - The interrupt attribute currently does not cause caller-saved VFP
   registers to be saved and restored if they are used, so putting
   __attribute__((interrupt)) on a called function doesn't prevent it
   from clobbering VFP state.
 - It is part of the -Wextra diagnostic group and can't be individually
   disabled when using -Wextra, which also means the diagnostic text of
   this specific warning appears in the documentation of -Wextra.

This change addresses all three issues by instead generating a warning
for any interrupt handler where the vfp feature is enabled. The warning
is
also given its own diagnostic group.

Closes #34876.

[clang][ARM] Emit an error when an interrupt handler is called.

Closes #95359.