bug#41242: Port feature/native-comp to Windows

[Eli Zaretskii]

> From: Nicolas Bértolo <nicolasbertolo@gmail.com>
> Date: Sat, 23 May 2020 14:47:03 -0300
> Cc: Andrea Corallo <akrl@sdf.org>, 41242@debbugs.gnu.org
> 
> Just to show some numbers:
> I run a fairly heavy Spacemacs configuration.
> Without any patch it takes 80 seconds to start.
> Reducing the number of probed files takes this down to 40 seconds.
> 
> The VTune profiler tells me it is spending 80% of the time waiting for 
> openp().

If it takes us 32 seconds to run openp, then how many files do we try
to probe?  32 sec is eternity!