timeout(1): Catch all signals and propagate them

The POSIX.1-2024 standard requires that timeout(1) utility propagate all
signals except SIGALRM, so timeout(1) needs to catch all signals for
this purpose. In addition, we need to separate those signals whose
default action is to terminate the program, because timeout(1) should
start the second timer for the kill signal if those signals are
received.

Obtained-from: DragonFly BSD
Reference: https://pubs.opengroup.org/onlinepubs/9799919799/utilities/timeout.html