Don't warn for undefined but used decls that are external because of a typedef.

This fixes pr14736. It is fairly ugly, but I don't think we can do much better
as we have to wait at least until the end of the typedef to know if the
function will have external linkage or not.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@171240 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed