[clang] [clang] Set correct FPOptions if attribute 'optnone' presents (PR #85605)

[Serge Pavlov via cfe-commits]

spavloff wrote:

Thanks!

> Is there any existing bookkeeping we no longer need to do if we're going to have this RAII object in scope during function parsing?

It seems handling fast-math is the only case that prevented using this RAII object.

https://github.com/llvm/llvm-project/pull/85605