Fix ldbl-128ibm ceill for non-default rounding modes (bug 19592).

The ldbl-128ibm implementation of ceill is only correct in
round-to-nearest mode (in other modes, there are incorrect results and
overflow exceptions in some cases).  It is also unnecessarily
complicated, rounding both high and low parts to the nearest integer
and then adjusting for the semantics of ceil, when it seems more
natural to take the ceiling of the high part (__ceil optimized inline
versions can be used), and that of the low part if the high part is an
integer, as was done for floorl.  This patch makes it use that simpler
approach.

Tested for powerpc.

	[BZ #19592]
	* sysdeps/ieee754/ldbl-128ibm/s_ceill.c (__ceill): Use __ceil on
	high and low parts then use ldbl_canonicalize_int if needed.