test-lib: rely on logs to detect leaks

test-lib: rely on logs to detect leaks

When we run with sanitizers, we set abort_on_error=1 so that the tests
themselves can detect problems directly (when the buggy program exits
with SIGABRT). This has one blind spot, though: we don't always check
the exit codes for all programs (e.g., helpers like upload-pack invoked
behind the scenes).

For ASan and UBSan this is mostly fine; they exit as soon as they see an
error, so the unexpected abort of the program causes the test to fail
anyway.

But for LSan, the program runs to completion, since we can only check
for leaks at the end. And in that case we could miss leak reports. And
thus we started checking LSan logs in faececa53f (test-lib: have the
"check" mode for SANITIZE=leak consider leak logs, 2022-07-28).
Originally the logs were optional, but logs are generated (and checked)
always as of 8c1d6691bc (test-lib: GIT_TEST_SANITIZE_LEAK_LOG enabled by
default, 2024-07-11). And we even check them for each test snippet, as
of cf1464331b (test-lib: check for leak logs after every test,
2024-09-24).

So now aborting on error is superfluous for LSan! We can get everything
we need by checking the logs. And checking the logs is actually
preferable, since it gives us more control over silencing false
positives (something we do not yet do, but will soon).

So let's tell LSan to just exit normally, even if it finds leaks. We can
do so with exitcode=0, which also suppresses the abort_on_error flag.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>