[Bug 47791] New: Inconsistent %ERRORLEVEL% after setting env var value in cmd.exe

[WineHQ Bugzilla]

https://bugs.winehq.org/show_bug.cgi?id=47791

Bug ID: 47791
           Summary: Inconsistent %ERRORLEVEL% after setting env var value
                    in cmd.exe
           Product: Wine
           Version: 4.16
          Hardware: x86
                OS: Linux
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: cmd
          Assignee: [e-mail]
          Reporter: [e-mail]
      Distribution: ---

Deleting an environment variable on cmd.exe seems to return %ERRORLEVEL% 1,
while on windows' cmd.exe it returns 0.

This matters because some core visual studio scripts like vsdevcmd.bat rely on
this behavior to set the environment properly. Note that using windows' cmd on
wine (using winetricks cmd) yields the same incorrect results.

On wine's cmd.exe
-----------------

wineuser@b081d9035bff:/$ wine cmd
Microsoft Windows 10.0.10240

Z:>set DOES_NOT_EXIST=

Z:>echo %ERRORLEVEL%
1

On windows 10's cmd.exe
-----------------------

Microsoft Windows [Version 10.0.17763.379]
(c) 2018 Microsoft Corporation. All rights reserved.

C:\Users\IEUser>set DOES_NOT_EXIST=

C:\Users\IEUser>echo %ERRORLEVEL%
0