Fix ldbl-128ibm sinhl inaccuracy near 0 (bug 18789).

ldbl-128ibm sinhl uses a too-big threshold to decide when to return
the argument, resulting in large errors.  This patch fixes it to use a
more appropriate threshold.

Tested for x86_64, x86 and powerpc.

	[BZ #18789]
	* sysdeps/ieee754/ldbl-128ibm/e_sinhl.c (__ieee754_sinhl): Use
	smaller threshold for returning the argument.
	* math/auto-libm-test-in: Add more tests of sinh.
	* math/auto-libm-test-out: Regenerated.
	* sysdeps/i386/fpu/libm-test-ulps: Update.