MFC r358553: hexdump: tests: take into account byte order

Hexdump test was failling on big endian systems when testing decimal, octal
and hexa outputs as the tests were designed on a little endian system. This
revision adds the two distinct flavors of output expected and determines at
runtime which to compare against.

MFC r328188,r328189,r328200: Fix wrong output for multibyte corner cases

MFC r328188: od(1): Fix wrong output for corner cases in multibyte locales.

Restore the original character to print if we used the look-ahead
buffer, but that didn't help -- we either got an illegal sequence
or still can't complete.

MFC r328189: od(1): Fix mis-patch from r328188

od_test.sh got duplicated erroneously when it was added in r328188. Dedup.

MFC r328200: Silence the gcc warning: 'op' may be used uninitialized in this
function

PR: 224552

MFC r320930,r324286: Add tests for hexdump(1)

MFC r320930:
Add some basic tests for hexdump(1)'s various output flags. Formatting
tests are omitted for this initial run as there are still some bugs to work
out there.

This covers -s flag testing on devices and non-devices that would have
caught breakage found in PR 219173 as well as other subtle breakage caused
locally.

MFC r324286: hexdump: Remove expected test failures for now succeeding tests

r323990 fixed the -s flag breakage reported by PR 219173. Mark the
corresponding hexdump tests accordingly, since they should now both succeed.

PR: 222781

Add some basic tests for hexdump(1)'s various output flags. Formatting
tests are omitted for this initial run as there are still some bugs to work
out there.

This covers -s flag testing on devices and non-devices that would have
caught breakage found in PR 219173 as well as other subtle breakage caused
locally.

Reviewed by: cem, ngie
Approved by: cem (acting co-mentor)
MFC after: 2 weeks
Differential Revision: https://reviews.freebsd.org/D11279