These cases occur frequently for declarations in the global module (above the
module-declaration) in a Modules TS module interface. When we merge a
definition from another module into such a module-private definition, ensure
that we transitively make everything lexically within that definition visible
to that translation unit.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@307129 91177308-0d34-0410-b5e6-96231b3b80d8