brush should ignore SIGTERM in interactive mode

[oech3]

fish> bash -c 'kill -SEGV $$'
fish: Job 1, 'bash -c 'kill -SEGV $$'' terminated by signal SIGSEGV (Address boundary error)
fish>  brush -c 'kill -SEGV $$' # exit 0

[oech3]

On the other hand,

bash$ kill $$ # do nothing
brush$ kill $$
fish: Job 1, 'brush' terminated by signal SIGKILL (Forced quit)

[reubeno]

It looks like brush isn't ignoring SIGTERM in interactive mode (but should). That's definitely a compat bug we should resolve. As part of it, we should also reevaluate the general signal ignoring policy.

Regarding SIGSEGV, it looks like rust's standard library may handle SIGSEGV (see this). I can't think of legitimate cases for sending SIGSEGV to a process, off the top of my head -- so it's a behavioral difference, but not one that is worth trying to address unless we get evidence to the contrary.

[oech3]

I agree with SIGSEGV is not important. I leave
https://github.com/uutils/coreutils/blob/f52e3e800bb5bd429f10c34cb86b997e33a670e0/src/uucore/src/lib/lib.rs#L149-L166
for the sake.

This might problem for some restricted containers:

> strace -o /dev/null -e inject=/sigaction:error=EPERM brush
fatal runtime error: assertion failed: signal(libc::SIGPIPE, handler) != libc::SIG_ERR, aborting

We cannot fix it without std's change.