[flang] Configure FirOpBuilder based on math driver options.

Added MathOptionsBase to share fastmath config between different
components. Frontend driver translates LangOptions into MathOptionsBase.
FirConverter configures FirOpBuilder using MathOptionsBase
config passed to it via LoweringOptions.

Depends on D137390

Reviewed By: jeanPerier

Differential Revision: https://reviews.llvm.org/D137391