[flang] Add -J and -module-dir to f18 driver

Add -J to the f18 driver for compatibility with gfortran.
Add -module-dir for compatibility with the new flang driver.

They both set the output directory for .mod files and add the
directory to the search list. -module still only does the former.

Clean up the new driver test to match.

Differential Revision: https://reviews.llvm.org/D97164