This reverts commit r284176. It still marks some modules as invisible
that should be visible. Will follow up with the author with a test case.
llvm-svn: 284382
compiles without -fmodules-local-submodule-visibility. Original commit message:
[modules] When merging one definition into another, propagate the list of
re-exporting modules from the discarded definition to the retained definition.
llvm-svn: 284176