SIGABRT/SIGIOT confusion under Linux

[Nate Eldredge <nate@xxxxxxxxxxxxxxxxxxxx>]

On Linux, the obscure SIGIOT signal, which hasn't really been meaningful 
on any machine since the PDP-11, is an alias for the common SIGABRT 
(signal 6).  The system strsignal() function maps signal 6 to the expected 
description "Aborted".  However, since zsh does its own translation, and 
since the SIGABRT precedes SIGIOT in Linux's <signal.h>, the latter 
overwrites the former in zsh's signal string tables.  See 
Src/signames2.awk.

This has (at least) two unfortunate results:

1. When a command aborts by calling `abort()`, which raises SIGABRT, zsh 
emits the message "zsh: IOT instruction (core dumped)" which will surely 
mystify most users.

2. The `kill` builtin doesn't accept `-ABRT`.  If you wanted to send the 
abort signal to a process, you would have to know to do `kill -IOT pid` 
instead, or `kill -6 pid` if you have the numbers memorized.

Tested with zsh 5.9 as distributed with Ubuntu 22.10 on x86-64, but the 
latest zsh source in git seems to not have changed.

--
Nate Eldredge
nate@xxxxxxxxxxxxxxxxxxxx