Work around a crash when checking access to injected class names

Work around a crash when checking access to injected class names
qua templates.  The current fix suppresses the access check entirely
in this case;  to do better, we'd need to be able to say that a
particular lookup result came from a particular injected class name,
which is not easy to do with the current representation of LookupResult.
This is on my known-problems list.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@111009 91177308-0d34-0410-b5e6-96231b3b80d8