Synchronize the logic for deciding to link a gv.

We were deciding to not link an available_externally gv over a
declaration, but then copying over the body anyway.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@255169 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed