Don't crash on redefinitions.

One error we were not deleting the alias or putting it in the Module. The
end result is that there was an use left of the aliasee when the module was
deleted.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@208447 91177308-0d34-0410-b5e6-96231b3b80d8