Look through using decls when checking whether a name is an acceptable
nested-name specifier name.

I accidentally checked in the test case for this in the last commit ---
fortunately, that refactor was inspired by having debugged this problem already,
so I can fix the bug quick (though probably not fast enough for the buildbots).



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@91677 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed