[Bug 45320] cmd creates an environment variable with an empty name

https://bugs.winehq.org/show_bug.cgi?id=45320

--- Comment #4 from Jason Edmeades  ---
My gut feeling is that CreateProcess itself should be setting the =C: type
environment variable, but nothing has ever cared that it doesnt so its not
worth implementing. In cmd we needed a way to remember the current directory
for any other drive letter you visited, so using the same mechanism made sense,
hence setting it explicitly at cmd start.

Since Python doesnt like it, I guess you need to look at how Python retrieves
and enumerates its copy of the environment to see which API potentially masks
these out (assuming this works on windows). Alternatively is the env block
passed into a launched process excluding these somehow?