detect-virt: also detect "microsoft" as WSL
    
    From https://github.com/microsoft/WSL/issues/423#issuecomment-221627364:
    > it's unlikely we'll change it to something that doesn't contain "Microsoft"
    > or "WSL".
    
    ... but well, it happened. If they change it incompatibly w/o adding an stable
    detection mechanism, I think we should not add yet another detection method.
    But adding a different casing of "microsoft" is not a very big step, so let's
    do that.
    
    Follow-up for #11932.
    
    (cherry picked from commit a2f838d59075a49b012f9b7056664f7ffeed44d2)