浮点异常-gcc错误？

#include <fenv.h>
#include <stdio.h>
int main()
{
    #pragma STDC FENV_ACCESS ON
    1.0/0.0;
    printf(\"%x\\n\", fetestexcept(FE_ALL_EXCEPT));
}

main

double x = 1.0/0.0;

-Wall

f.c:5:0: warning: ignoring #pragma FENV_ACCESS ON [-Wunknown-pragmas]

* `The default state for the `FENV_ACCESS\' pragma (C99 7.6.1).\'

 This pragma is not implemented, but the default is to \"off\" unless
 `-frounding-math\' is used in which case it is \"on\".

gcc -O0

gcc -O3