... I'm committing the below. Tested x86_64-linux. Thanks, Paolo.
/////////////////
2015-08-19 Paolo Carlini <paolo.carl...@oracle.com> * include/c_global/cmath: Revert fix for libstdc++/58625, no longer necessary (__builtin_signbit is now type-generic).
Index: include/c_global/cmath =================================================================== --- include/c_global/cmath (revision 227003) +++ include/c_global/cmath (working copy) @@ -650,10 +650,10 @@ isnormal(_Tp __x) { return __x != 0 ? true : false; } - // The front-end doesn't provide a type generic builtin (libstdc++/58625). + // Note: c++/36757 is fixed, __builtin_signbit is type-generic. constexpr bool signbit(float __x) - { return __builtin_signbitf(__x); } + { return __builtin_signbit(__x); } constexpr bool signbit(double __x) @@ -661,7 +661,7 @@ constexpr bool signbit(long double __x) - { return __builtin_signbitl(__x); } + { return __builtin_signbit(__x); } template<typename _Tp> constexpr typename __gnu_cxx::__enable_if<__is_integer<_Tp>::__value,