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

[Serge Pavlov via cfe-commits]

spavloff wrote:

A little about the significance of this fix. To implement pragma FENV_ROUND, we need to apply the FP options stored in the instance of CompoundStmt to the builder object, so that it uses the specified rounding mode. It can be done using the class CGFPOptionsRAII. However in this case a couple of issues rise, both related to fast-math. This patch is intended to fix one of them an is a prerequisite for pragma FENV_ROUND implementation.

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