Bug#617894: [ARMel] tgammal isn't accurate enough

[Julien PUYDT <julien.puydt@laposte.net>]

Package: libc6
Version: 2.11.2-13

The following piece of code :

#include <stdio.h>
#include <math.h>

int
main (int argc,
      char* argv[])
{
  long double x = 6.0;
  printf ("tgammal (%20Lf)=%20Lf\n", x, tgammal (x));
  return 0;
}

Prints, on an x86 debian unstable (eglibc 2.11.2-11) :
tgammal (            6.000000)=          120.000000
And on an ARMel debian unstable (eglibc 2.11.2-13) :
tgammal (6.00000000000000000000)=119.99999999999997157829

That last results if of too poor precision for sage 
(http://www.sagemath.org), which I'm porting to the platform.

The box used to run ubuntu, where the problem occurred too 
(https://bugs.launchpad.net/ubuntu/+source/eglibc/+bug/713985).

Snark on #sage-devel