Fix ldbl-128ibm sinhl spurious overflows (bug 19350).

The ldbl-128ibm implementation of sinhl uses a slightly too small
overflow threshold (similar to bug 16407 for coshl).  This patch fixes
it to use a safe threshold (so that values whose high part is above
the value compared with definitely result in an overflow in all
rounding modes).

Tested for powerpc.

	[BZ #19350]
	* sysdeps/ieee754/ldbl-128ibm/e_sinhl.c (__ieee754_sinhl):
	Increase overflow threshold.