The testsuite already contains quite a number of SIGCHLD handler
installation/un-installations. Here is my attempt at an inventary.
1. complete-run.pl installs a SIGCHLD handler in the `start_xserver()` function
call, which prints an error and exits when all x server processes have exited.
2. In the TestWorker child process, a SIGCHLD handler is installed to reap dead
test child processes.
3. The TestWorker child process forks another child process for running the test
file, where the previously installed SIGCHLD handler (point 2) is unset.
This is where this commit comes in: it installs a SIGCHLD handler in the test
file child process, which will trigger when the i3 subprocess dies.
4. (For completeness: i3test.pm defines an END block where it unsets the
previous SIGCHLD handler before it kills the subprocesses.)
With this commit, when i3 segfaults, the output will look like this:
Writing logfile to 'testsuite-2022-09-10-21-14-46-4.20-103-gb242bceb/complete-run.log'...
[:100] /home/michael/i3/testcases/t/167-workspace_layout.t: BAILOUT
completed 0 of 1 tests
test /home/michael/i3/testcases/t/167-workspace_layout.t bailed out:
could not kill i3: No such process
fixes https://github.com/i3/i3/issues/4437
f795c2c8da