[Bug 46545] New: WINEPREFIX doesn't work when ends with "windows"

https://bugs.winehq.org/show_bug.cgi?id=46545

Bug ID: 46545
           Summary: WINEPREFIX doesn't work when ends with "windows"
           Product: Wine
           Version: 4.0
          Hardware: x86-64
                OS: Linux
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: -unknown
          Assignee: [e-mail]
          Reporter: [e-mail]
      Distribution: ---

Created attachment 63407
  --> https://bugs.winehq.org/attachment.cgi?id=63407
wine default prefix

Setting WINEPREFIX to something that ends with "windows" (e.g., $HOME/windows)
causes wineboot to create a broken wine instance.

In particular, C:\ won't exist, for example:
> ~ wine cmd /C dir 'C:'
> Volume in drive C has no label.
> Volume Serial Number is 0000-0000
>
> Directory of C:
>
> File not found.

whereas with the default prefix C:\ is fine:
> ~ wine cmd /C dir 'C:'
> Volume in drive C has no label.
> Volume Serial Number is 0000-0000
>
> Directory of C:
>
> 1/28/2019  11:31 AM  <DIR>         Program Files
>  1/28/2019  11:31 AM  <DIR>         Program Files (x86)
>  1/28/2019  11:31 AM  <DIR>         ProgramData
>  1/28/2019  11:31 AM  <DIR>         users
>  1/28/2019  11:31 AM  <DIR>         windows
>        0 files                        0 bytes
>        5 directories     90,299,498,496 bytes free

Setting WINEPREFIX to other values seems to work fine (e.g., $HOME/win).  Why
is "windows" special?  Are there any other special values that WINEPREFIX
shouldn't use?

See the attached console log for more details.