[modules] If we load two declarations with typedef names for linkage purposes

on top of a local declaration of the same entity, we still need to remember
that we loaded the first one or we may fail to merge the second one properly.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@226765 91177308-0d34-0410-b5e6-96231b3b80d8