powl yields NaN instead of +0

[zimmermann6]

for x=0x1.98p-3072l and y=0xa.ab43b6dba9a6383p+16364l, powl yields NaN instead of +0 (even with only one thread, cf
#222)

zimmerma@coriandre:~/svn/tbd/20/src/binary80$ cat test2_pow_openlibm.c
#include <stdio.h>
#include <math.h>
#include <omp.h>

int main()
{
long double x = 0x1.98p-3072l;
long double y = 0xa.ab43b6dba9a6383p+16364l;
long double z;
z = powl (x, y);
printf ("z=%La\n", z);
return 0;
}

zimmerma@coriandre:/svn/tbd/20/src/binary80$ gcc -fno-builtin test2_pow_openlibm.c /localdisk/zimmerma/openlibm-0.8.7/libopenlibm.a
zimmerma@coriandre:/svn/tbd/20/src/binary80$ ./a.out
z=-nan

zimmerma@coriandre:/svn/tbd/20/src/binary80$ gcc -fno-builtin test2_pow_openlibm.c -lm # with GNU libc
zimmerma@coriandre:/svn/tbd/20/src/binary80$ ./a.out
z=0x0p+0