modf different behavior on gcc 4.9.0-6 VS at 8.0 on a POWER8 machine

gistfile1.txt

[root@ 64b 13:44:10 /tmp/modf]$ uname -m
ppc64le
[root@ 64b 13:44:17 /tmp/modf]$ cat /proc/cpuinfo
processor       : 0
cpu             : POWER8E (raw), altivec supported
clock           : 3425.000000MHz
revision        : 2.1 (pvr 004b 0201)

timebase        : 512000000
platform        : pSeries
model           : IBM pSeries (emulated by qemu)
machine         : CHRP IBM pSeries (emulated by qemu)
[root@ 64b 13:44:19 /tmp/modf]$ /opt/at8.0/bin/gcc --version
gcc (GCC) 4.9.2 20141013 (Advance-Toolchain-at8.0) [ibm/gcc-4_9-branch, revision: 216164 merged from gcc-4_9-branch, revision 216151]
Copyright (C) 2014 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

[root@ 64b 13:44:27 /tmp/modf]$ gcc --version
gcc (Debian 4.9.0-6) 4.9.0
Copyright (C) 2014 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

[root@ 64b 13:44:31 /tmp/modf]$ cat modf.c
#include<stdio.h>
#include<math.h>

int main ()
{
   double x, fractpart, intpart;

   x = 8.123456;
   fractpart = modf(x, &intpart);
   printf("%16lf : Integral part = %16lf\tFraction Part = %16lf\n", x, intpart, fractpart);

   x = -8.123456;
   fractpart = modf(x, &intpart);
   printf("%16lf : Integral part = %16lf\tFraction Part = %16lf\n", x, intpart, fractpart);

   x = 8;
   fractpart = modf(x, &intpart);
   printf("%16lf : Integral part = %16lf\tFraction Part = %16lf\n", x, intpart, fractpart);

   x = -8;
   fractpart = modf(x, &intpart);
   printf("%16lf : Integral part = %16lf\tFraction Part = %16lf\n", x, intpart, fractpart);

   return(0);
}
[root@ 64b 13:44:36 /tmp/modf]$ gcc modf.c -o modf.gcc
[root@ 64b 13:44:59 /tmp/modf]$ /opt/at8.0/bin/gcc modf.c -o modf.at
[root@ 64b 13:45:07 /tmp/modf]$ ./modf.gcc
        8.123456 : Integral part =         8.000000     Fraction Part =         0.123456
       -8.123456 : Integral part =        -8.000000     Fraction Part =        -0.123456
        8.000000 : Integral part =         8.000000     Fraction Part =         0.000000
       -8.000000 : Integral part =        -8.000000     Fraction Part =         0.000000
[root@ 64b 13:45:12 /tmp/modf]$ ./modf.at
        8.123456 : Integral part =         8.000000     Fraction Part =         0.123456
       -8.123456 : Integral part =        -8.000000     Fraction Part =        -0.123456
        8.000000 : Integral part =         8.000000     Fraction Part =         0.000000
       -8.000000 : Integral part =        -8.000000     Fraction Part =        -0.000000

## Note the -0.0 on at8.0!! ##