* sysdeps/ieee754/ldbl-128ibm/s_nextafterl.c (nextafterl): Remove
unused ily variable. Fix nextafterl on +-__LDBL_MAX__ and +-Inf.
Remove unreachable code at the end.
* sysdeps/ieee754/ldbl-128ibm/s_fpclassifyl.c: Correct description of
ldbl-128ibm in comment.
(fpclassifyl): Correct classification of denormals.
* sysdeps/ieee754/ldbl-128ibm/s_nextafterl.c (nextafterl): Correct
return value for MIN denormal. Rewrite using long double math too
correctly handle denormals and canonicalize the results.