Don't include math.h/math_private.h in math_ldbl_opt.h.
The sysdeps/ieee754/ldbl-opt version of math_ldbl_opt.h includes
math.h and math_private.h, despite not having any need for those
headers itself; the sysdeps/generic version doesn't. About 20 files
are relying on math_ldbl_opt.h to include math.h and/or math_private.h
for them, even though none of them necessarily used on a platform that
needs ldbl-opt support.
* sysdeps/ieee754/ldbl-opt/math_ldbl_opt.h: Don't include
math.h or math_private.h.