If we encounter a friend class template for which we cannot resolve

the nested-name-specifier (e.g., because it is dependent), do not
error even though we can't represent it in the AST at this point.

This is a horrible, horrible hack. The actual feature we still need to
implement (for C++98!) is covered by PR12292. However, we used to
silently accept this code, so when we recently started rejecting it we
caused some regressions (e.g., <rdar://problem/11147355>). This hack
brings us back to the passable-but-not-good state we had previously.

llvm-svn: 153752