The numbers of signals vary by arch. On the common arches the signals
listed here all use the same numbers, but people are likely to use
this on more fringe architectures too, so let's use symbolic names
instead.
Also the comment about gdb "hitting the same kill" didn't make sense.
The syntax is a bit baroque, but using a helper variable does not work.
Also shellcheck complains about $[ ] which would have made this more
legible.
meson test --wrapper hook to print a gdb backtrace inline in the test
log when a test exits with an actual crash signal (SIGSEGV, SIGABRT,
SIGBUS, SIGFPE, SIGILL). Wired into the default add_test_setup() so it
runs automatically on every `meson test`.
Environmental terminations (SIGTERM/SIGKILL/SIGPIPE/SIGALRM) are passed
through without replay, and the original signal is re-raised so the
parent's wait() observes WIFSIGNALED rather than a plain exit code.