[Flang] Add debug flag to enable current debug information pass
While a pass exists to generate basic debug information, currently there is not a corresponding flag to enable it.
This patch adds support for activating this pass at any debug level >= -g1, as well as emiting a warning for higher levels that the functionality is not yet fully implemented.
This patch also adds -g and -gline-tables-only to appear when `flang-new` --help is run
Depends on D142347.
Reviewed By: awarzynski
Differential Revision: https://reviews.llvm.org/D146814
13 files changed: