forward declarations.
Especially with template instantiations, there are legitimate reasons
why for declarations might be emitted into a DW_TAG_module skeleton /
forward-declaration sub-tree, that are not forward declarations in the
sense of that there is a more complete definition over in a .pcm file.
The example in the testcase is a constant DW_TAG_member of a
DW_TAG_class template instatiation.
rdar://problem/43623196
llvm-svn: 341123
