When we're linking an alias which will be defined later, we neeed to
build a GlobalAlias, or else we'll crash later in
IRLinker::linkGlobalValueBody.
clang sometimes constructs aliases like this for C++ destructors.
Differential Revision: https://reviews.llvm.org/D49316
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@337053 91177308-0d34-0410-b5e6-96231b3b80d8