[BE] Print backtraces from coredumps (#89309)
By simply invoking `gdb python core -ex "bt" -ex "q"`
Test plan:
See: [linux-focal-py3.7-gcc7 / test (default, 1, 2, linux.2xlarge)](https://github.com/pytorch/pytorch/actions/runs/3500498821/jobs/5863369649#step:14:39)
Not sure why multiprocessing tests SEGFAULT, but they do
Pull Request resolved: https://github.com/pytorch/pytorch/pull/89309
Approved by: https://github.com/clee2000, https://github.com/huydhn
