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 17:30:40 +0000
> 
> > Great, thanks for trying this.  So at the very least we have a
> > workaround, if not the solution.
> 
> Yes. It also seemed faster, in that I had to be quicker at entering
> process IDs to send a single before the subprocess exited normally.

Maybe because when w32-start-process-share-console is nil, we tell
CreateProcess to create a new console for the sub-process, and that
takes more time for the OS.