The goal of this commit is to get just enough Sema support to recognize Objective-C classes
as types. That said, the AST nodes ObjcInterfaceDecl, ObjcInterfaceType, and ObjcClassDecl are *very*
preliminary.

The good news is we no longer need -parse-noop (aka MinimalActions) to parse cocoa.m.

llvm-svn: 41752