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

Attribute `optnone` must turn off all optimizations including fast-math
ones. Actually AST nodes in the 'optnone' function still had fast-math
flags. This change implements fixing FP options before function body is
parsed.

GitOrigin-RevId: a04624206ddf03dc54d5c372e7eac13575b4124b
10 files changed