[llvm] r183354 - Rename operator== parameter to `RHS`.

[Rafael Espíndola]

> Minor pedantry, if you're here - ideally this (& any other op overload
> members that can be) should be a non-member. (for one thing, this op==
> only accepts a non-const LHS (but the other thing is that having it as
> a non-member keeps the behavior symmetric in cases of implicit
> conversion of operands, etc))

r183539.

Cheers,
Rafael