V3 PATCH: #undef some C99 math macros in <cmath>

[Benjamin Kosnik]

> | > > + #undef isgreater
> | > > + #undef isgreaterequal
> | > > + #undef isless
> | > > + #undef islessequal
> | > > + #undef islessgreater
> | > > + #undef isunordered
> | > 
> | > in the short term, this is acceptable.
> | 
> | This is what you always will have to do.  C99 demands that these are
> | macros.  You'll replace them with template functions after undefining
> | the macros.  There is not more correct way.

Ok. I stand corrected. 

I didn't mean _USE_GNU, I meant this:

#define _GNU_SOURCE 1

this is unconditionally defined in config/os/gnu-linux/bits/os_defines.h

Obviously, this is not such a smooth idea, as it leads to the problems
 that you are experiencing.

> Where should we put those? In the global namespace or in the std::?
> Strictly speaking, we're not allowed to put them in the global
> namespace.

Ugh. I think conditionally putting them into std:: makes the most sense, 
as eventually they will wind up there, correct? Then if users enable c99 
support, they could have access to these functions.

-benjamin