dup'ing stdout is detectable on Windows

[dra27]

In order to guarantee no output from the solver when verbosity is switched off, we have:

https://github.com/AltGr/ocaml-mccs/blob/b46f1df8d9ef9dfe7c153cc10198a0b1ff2fca36/src/glpk_solver.cpp#L76-L79

followed by:

https://github.com/AltGr/ocaml-mccs/blob/b46f1df8d9ef9dfe7c153cc10198a0b1ff2fca36/src/glpk_solver.cpp#L127-L130

This operation is undetectable on Unix but detectable on Windows, because it invalidates the underlying console handle. Detected in https://github.com/ocaml/opam/pull/4710. It's fixed more reliably there, but I think it would be better to ensure that the patched GLPK, etc. never leaks by improving the verbosity checking rather than preventing the handle from being used.

[kit-ty-kate]

Related to https://github.com/ocaml-opam/ocaml-mccs/pull/50