[OpenMP][NFC] Add an option to print the module before in OpenMPOpt

Previously there was a debug flag to print the module after
optimizations. Sometimes we wanted to print the module before
optimizations so this is being split into two flags.
`-openmp-opt-print-module` is now `-openmp-opt-print-module-after`.

Reviewed By: jdoerfert

Differential Revision: https://reviews.llvm.org/D120768