The following C++ file fails to build with GCC 6:

#include <cmath>
#include <iostream>

int main(int argc, char *argv[])
{
  double num = 0.0;
  std::cout << std::isnan(num) << "\n";
  return 0;
}

This throws the following compile time error:

> test.cpp: In function ���int main(int, char**)���:
> test.cpp:7:16: error: ���__builtin_isnan��� is not a member of ���std���
>    std::cout << std::isnan(num) << "\n";
>                 ^~~
> test.cpp:7:16: note: suggested alternative:
> <built-in>: note:   ���__builtin_isnan���

Is that meant to happen? It builds properly with GCC 7.

Build command: g++-6 -O2 -Wall -g test.cpp