Don't exclude i386 from LDBL_MANT_DIG == 64; it works properly in
that case.
While here, replace strcmp + atf_tc_fail with ATF_CHECK_MSG for 2
reasons:
- Gather as many results as possible instead of failing early and
not testing the rest of the cases.
- Simplify logic when checking test inputs vs outputs and printing
test result.
Tested on: amd64, i386
MFC after: 1 week
Sponsored by: Dell EMC Isilon
