gettext tests: don't ignore "test-tool regex" exit code

Amend a prerequisite check added in 5c1ebcca4d1 (grep/icase: avoid kwsset on literal non-ascii strings, 2016-06-25) to do invoke 'test-tool regex' in such a way that we'll notice if it dies under SANITIZE=leak due to having a memory leak, as opposed to us not having the "ICASE" support we're checking for. Because we weren't making a distinction between the two I'd marked these tests as passing under SANITIZE=leak in 03d85e21951 (leak tests: mark remaining leak-free tests as such, 2021-12-17). Doing this is tricky. Ideally "test_lazy_prereq" would materialize as a "real" test that we could check the exit code of with the same signal matching that "test_must_fail" does. However lazy prerequisites aren't real tests, and are instead lazily materialized in the guts of "test_have_prereq" when we've already started another test. We could detect the abort() (or similar) there and pass that exit code down, and fail the test that caused the prerequisites to be materialized. But that would require extensive changes to test-lib.sh and test-lib-functions.sh. Let's instead simply check if the exit code of "test-tool regex" is zero, and if so set the prerequisites. If it's non-zero let's run it again with "test_must_fail". We'll thus make a distinction between "bad" non-zero (segv etc) and "good" (exit 1 etc.). Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>