[BUG] Wrong signal handling in subshells

[itislu]

It looks like the main signal handler is still the main process, not the subshell process.

SIGQUIT in this example should quit the entire subshell, not just cat:

(cat || echo 123)

We still print 123 in this example.

This issue also causes (cat) | (cat) to print too many newlines when Ctrl+C.

This also makes it apparent: (cat || echo 1 && exit 2) || echo $?

• (((cat))) also prints another newline for every subshell. - [BUG] minishell running in minishell prints too many newlines after exiting, also in subshells #257

[itislu]

Options to handle the main process differently:

1. Create a different handler function for the main process.
2. Don't kill the main process from child processes. -
   If sth goes bad in the main process it will just ft_clean_and_exit_shell.
3. Test if kill with negative pid fails if no child processes exist.
   If that's the case, check for that error and kill the current process instead.