bug#46494: 28.0.50; [native-comp] Problems with async background compile

[Eli Zaretskii]

> From: Andy Moreton <andrewjmoreton@gmail.com>
> Date: Sat, 20 Feb 2021 16:40:38 +0000
> 
> Using "(w32-start-process-share-console t)" with 'SIGHUP seemed to work
> without triggering the abort dialog, and killing emacs with async
> processes running also did, not trigger the aborts.

Great, thanks for trying this.  So at the very least we have a
workaround, if not the solution.

FTR, setting w32-start-process-share-console non-nil causes the
subprocess to start a new process group, and sending SIGHUP to the
inferior Emacs then kills it via the TerminateProcess API, whereas
when w32-start-process-share-console is nil (the default), we try
being nice, and send it the WM_CLOSE message.