Fix ldbl-128ibm ceill, rintl etc. for sNaN arguments (bug 20156).

Fix ldbl-128ibm ceill, rintl etc. for sNaN arguments (bug 20156).

The ldbl-128ibm implementations of ceill, floorl, roundl, truncl,
rintl and nearbyintl wrongly return an sNaN when given an sNaN
argument.  This patch fixes them to add such an argument to itself to
turn it into a quiet NaN.  (The code structure means this "else" case
applies to any argument which is zero or not finite; it's OK to do
this in all such cases.)

Tested for powerpc.

	[BZ #20156]
	* sysdeps/ieee754/ldbl-128ibm/s_ceill.c (__ceill): Add high part
	to itself when zero or not finite.
	* sysdeps/ieee754/ldbl-128ibm/s_floorl.c (__floorl): Likewise.
	* sysdeps/ieee754/ldbl-128ibm/s_rintl.c (__rintl): Likewise.
	* sysdeps/ieee754/ldbl-128ibm/s_roundl.c (__roundl): Likewise.
	* sysdeps/ieee754/ldbl-128ibm/s_truncl.c (__truncl): Likewise.