Add C++ special math functions to C++17

[Jonathan Wakely]

On 11 March 2016 at 16:31, Ed Smith-Rowland <3dw4rd@verizon.net> wrote:
> On 03/11/2016 10:55 AM, Jonathan Wakely wrote:
>>
>> The change approved in Jacksonville was to only add the special
>> functions to <cmath> and not <math.h>
>>
> That's easy.
> OK, since they changed that and the macro and made it nonconditional I
> should also drop the old-style macros __WANT_MATH_CANNEVERREMEMBER__ and the
> old-style version macro.
> So, in other words, we're *not* actually supporting TR29124 (that's fine by
> me).
> We can tweak the web pages.
> People on C++11, C++14 can use tr1.

I think we can keep 29124 support for pre-C++17, and for that case
<math.h> will include the functions (when the ICANNEVERREMEMBEREITHER
macro is defined).

> Did they keep the Cisms like:
>
>   float
>   foobarf(float x);
>
>   double
>   foobar(double x);
>
>   long double
>   foobarl(long double x);

Yes, I think so.

Let's do this after gcc6 though.