[flang] Make it easier to enable minimal FP output by default for module files...

[flang] Make it easier to enable minimal FP output by default for module files (but do not enable it)

Original-commit: flang-compiler/f18@f6b640319b33008375ca719a88fd0580bcf90bba
Reviewed-on: https://github.com/flang-compiler/f18/pull/671