Change ObjCInterfaceDecl to inherit from NamedDecl (not TypeDecl). While ObjCInterfac...

Change ObjCInterfaceDecl to inherit from NamedDecl (not TypeDecl). While ObjCInterfaceDecl is arguably a TypeDecl, it isn't a ScopedDecl. Since TypeDecl's are scoped, it makes sense to simply treat them as NamedDecl's. I could have fiddled a bit more with the hierarchy (in terms of creating a non-scoped TypeDecl), however this probably isn't worth the effort.

I also finished unifying access to scope decl change by converting Sema::getObjCInterfaceDecl() to use Sema::LookupDecl(). This is much cleaner now:-)

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@49107 91177308-0d34-0410-b5e6-96231b3b80d8