swift234

Don't diagnose failures to call symmetrically-typed binary operators
as a failure to convert the individual operand, since the operator
is likely conceptually generic in some way and the choice of any
specific overload is probably arbitrary.

Since we now fall back to a better-informed diagnostics point, take
advantage of this to generate a specialized diagnostic when trying to
compare values of function type with ===.

Fixes rdar://25666129.