[Bug 21338] New: cmd needs to set COMSPEC, PATHEXT, and PROMPT environment variables

http://bugs.winehq.org/show_bug.cgi?id=21338

Summary: cmd needs to set COMSPEC, PATHEXT, and PROMPT
                    environment variables
           Product: Wine
           Version: unspecified
          Platform: x86
        OS/Version: Linux
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: cmd
        AssignedTo: [e-mail]
        ReportedBy: [e-mail]

In Windows XP, if I start "cmd /c set" with an empty environment, I always get
these  variables:

COMSPEC=C:\WINDOWS\system32\cmd.exe
PATHEXT=.COM;.EXE;.BAT;.CMD;.VBS;.JS;.WS
PROMPT=$P$G

In Wine, however, cmd prints nothing. (I guess Wine sets those variables only
on startup, while Windows sets them in every instance of cmd.)

I tested it by running this Python script:

import subprocess
subprocess.Popen(["cmd", "/c", "set"], env={}).communicate()

(It just runs CreateProcess with "\0" as the environment, as far as I
understand.)

The problem I'm running into is: I run SCons, which starts a new Python script
in a mostly empty environment. The Python script calls os.popen, which relies
on COMSPEC to find "cmd.exe", and therefore fails.