[flang] Single entry point for GET_COMMAND_ARGUMENT

[rovka]

Summary

This patch refactors the runtime support for GET_COMMAND_ARGUMENT to
have a single entry point instead of 2. It also updates lowering
accordingly.

This makes it easier to handle dynamically optional arguments. See also
https://reviews.llvm.org/D118777

[jeanPerier]

Thanks a lot for following up on this. Beware that there is a test failure introduced in Runtime/no-cpp-dep.c (I think you need to remove the references to the removed runtime APIs there).
Otherwise LGTM.

flang/lib/Lower/IntrinsicCall.cpp

772–773

STATUS is also optional, I think it also needs to have handleDynamicOptional so that the OPTIONAL POINTER/OPTIONAL ALLOCATABLE edge case are handled correctly (I think the current code might unconditionally dereference the descriptor in these case).

[rovka]

Thanks for reviewing! I updated the patch. I'm not sure why the no-cpp-dep test was marked as unsupported for me locally, nuking the whole build directory seems to have fixed it though. Sorry about the noise there.