[RFA 2/4] Implement | (pipe) command.

[Eli Zaretskii]

> From: Philippe Waroquiers <philippe.waroquiers@skynet.be>
> Cc: Philippe Waroquiers <philippe.waroquiers@skynet.be>
> Date: Sat, 20 Apr 2019 23:21:51 +0200
> 
> +  if (shell_command_status > 0)
> +    {
> +      if (WIFEXITED (shell_command_status))
> +	warning (_("shell command \"%s\" exit status %d"), shell_command,
> +		 WEXITSTATUS (shell_command_status));
> +      else if (WIFSIGNALED (shell_command_status))
> +	warning (_("shell command \"%s\" exit with signal %d"), shell_command,
> +		 WTERMSIG (shell_command_status));

These macros will need to be ported to MinGW, since the current
definitions in gdb_wait.h are for Posix systems (and never used on
anything other than that).  Gnulib has replacements, but they are less
functional on Windows than I'd like them to be, in particular when the
shell program exited due to a signal.  I can provide better
replacements if you want.