With invalid overloaded operators, we can get into funny cases where

the overloading of member and non-member functions results in arity
mismatches that don't fit well into our overload-printing scheme. This
only happens for invalid code (which breaks the arity invariants for
these cases), so just suppress the diagnostic rather than inventing
anything new. Fixes <rdar://problem/9222009>.

llvm-svn: 130902