PR24030, PR24033: Consistently check whether a new declaration conflicts with

an existing using shadow declaration if they define entities of the same kind
in different namespaces.

We'd previously check this consistently if the using-declaration came after the
other declaration, but not if it came before.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@241428 91177308-0d34-0410-b5e6-96231b3b80d8