tests: avoid many spurious failures for shells with busted 'set -e'

tests: avoid many spurious failures for shells with busted 'set -e'

Some versions of the BSD Korn shell wrongly bail out when the
'errexit' shell flag is active and the left-hand command in a
"&&" list fails and that list is the *last* command of an entry
in a "case" statement.

* tests/defs (gcc, g++, gcj): Work around that.