Issue Description:

Given an enum, where one case has an associated value:

enum E {
 case a
 case b(Double)
 case c
}

When doing a comparison of a value v: E, as below:

if v != .c { … }

the compiler puts out this error message:

Referencing operator function '!=' on 'BinaryInteger' requires that 'E' conform to 'BinaryInteger'.

This error message is misleading since at no point is any reference to BinaryInteger or its = operator needs to be implemented or synthesised by declaring Comparable conformance.