[PATCH v2] Provide a C++ version of issignaling that does not use __MATH_TG

[Joseph Myers]

On Fri, 18 Aug 2017, Gabriel F. T. Gomes wrote:

> +/* There is no signaling_NaN for _Float128 in std::numeric_limits.
> +   Include ieee754_float128.h and use the bitfields in the union
> +   ieee854_float128.ieee_nan to build a signaling NaN.  */
> +#if __HAVE_FLOAT128
> +#include <ieee754_float128.h>
> +#endif

That needs to be __HAVE_DISTINCT_FLOAT128 (and so the other conditionals 
in this test need to be as well), since this internal header is in a 
sysdeps directory that won't be used for float128-as-ABI-alias.  Also note 
preprocessor indentation, "# include".

(In the C++ case, float128-as-ABI-alias will be a typedef for long double 
even with GCC 7 and later, so there's less need for C++ tests for it in 
that case.)

-- 
Joseph S. Myers
joseph@codesourcery.com