PR c++/36921 [4.3/4.4 Regression] warning "comparison does not have mathematical meaning" is not correct for overloaded operators that do not return boolean

[Jason Merrill]

I agree that we don't want to warn for this code, but I think the right 
place to fix it is in warn_about_parentheses; your patch will also 
disable the parenthesis warnings for overloaded comparison ops, which we 
don't want, since precedence is the same regardless of the return type.

Jason