pgsql: ci: Improve OpenBSD core dump backtrace handling.

ci: Improve OpenBSD core dump backtrace handling.

Since OpenBSD core dumps do not embed executable paths, the script now
searches for the corresponding binary manually within the specified
directory before invoking LLDB.  This is imperfect but should find the
right executable in practice, as needed for meaningful backtraces.

Author: Nazir Bilal Yavuz <byavuz81@gmail.com>
Discussion: https://postgr.es/m/CAN55FZ36R74TZ8RKsFueYwLxGKDAm3LU2FHM_ZUCSB6imd3vYA@mail.gmail.com
Backpatch-through: 18

Branch
------
master

Details
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https://git.postgresql.org/pg/commitdiff/b498af4204bd832e11ffc87fe1999f113cc29a87

Modified Files
--------------
.cirrus.tasks.yml               |  3 ++-
src/tools/ci/cores_backtrace.sh | 31 +++++++++++++++++++++++++++----
2 files changed, 29 insertions(+), 5 deletions(-)