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

[Nicolas Bértolo]

> We would need to change `package-delete` though. It would no longer fully
> delete the directory. Maybe other functions in `package.el` would need
> to be updated to deal with these changes.

Maybe not. We could move the .eln to the parent of the argument to
`delete-directory`.

For example move

elpa\28.0\develop\company-20200510.1614\eln-x86_64-w64-mingw32-683c5a1b96c51930\company.eln

to

elpa\28.0\develop\company.eln.old

The code to find the .eln.old files to delete would have to check if
it is a package it is dealing with and search for .eln.old files in an
upper folder.

Nicolas.