CI: work around LeakSanitizer crashes with use_tls=0

Without this fix, we have randomly been getting CI failures due to
LeakSanitizer itself crashing after all the tests in a program have
succeeded. This has been happening randomly for a long time, but
!1486
made it very reliably repeatable in the job x86_64-debian-full-build
(and no other job) in the test-subsurface-shot program.

--- Fixture 2 (GL) ok: passed 4, skipped 0, failed 0, total 4
Tracer caught signal 11: addr=0x1b8 pc=0x7f6b3ba640f0 sp=0x7f6b2cc77d10
==489==LeakSanitizer has encountered a fatal error.

I was also able to get a core file after twiddling, but there it ended
up with lsan aborting itself rather than a segfault.

We got some clues that use_tls=0 might work around this, from
https://github.com/google/sanitizers/issues/1342
https://github.com/google/sanitizers/issues/1409
and some other projects that have cargo-culted the same workaround.

Using that cause more false leaks to appear, so they need to be
suppressed. I suppose we are not interested in catching leaks in glib
using code, so I opted to suppress g_malloc0 altogether. Pinpointing it
better might have required much more slower stack tracing.

wl_shm_buffer_begin_access() uses TLS, so no wonder it gets flagged.

ld-*.so is simply uninteresting to us, and it got flagged too.

Since this might have been fixed already in LeakSanitizer upstream, who
knows, leave some notes to revisit this when we upgrade that in CI.

This fix seems to make the branch of
!1486


in my quick testing.

Suggested-by: Derek Foreman <derek.foreman@collabora.com>
Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.com>