[v3] Use Solaris prototypes if possible (PR libstdc++-v3/1773)

[Paolo Carlini]

Hi,
> Actually, could someone please append to this comment in tr1/cmath:
>
>   // Note: we deal with fabs in a special way, because an using std::fabs
>   // would bring in also the overloads for complex types, which in C++0x
>   // mode have a different return type.
>
> Something like:
>
>   // With __CORRECT_ISO_CPP_MATH_H_PROTO1, math.h imports std::fabs in 
> the
>   // global namespace after the declarations of the float / double / long
>   // double overloads but before the std::complex overloads.
>
> so we remember why it works, why it breaks if users do silly things, 
> and what needs changing if another platform tries to define 
> __CORRECT_ISO_CPP_MATH_H_PROTO1.

Done, thanks!

Paolo.