tests: SKIP backtrace-data and backtrace-dwarf on unsupported arches.

run-backtrace-data.sh did check stderr whether the arch was unsupported
but the test didn't print that message yet. backtrace-dwarf did print
the message but was missing a check_unsupported test. Also add an explicit
check_main test for backtrace-dwarf.

Signed-off-by: Mark Wielaard <mjw@redhat.com>
3 files changed