Changes needed for compilation using MSVC in Windows: small change to a CHECK due to missing iostream overload.
Changes needed for compilation using MSVC in Windows: small change to a CHECK due to missing iostream overload.

PiperOrigin-RevId: 418756761
Change-Id: I8d73f8a0262950c4b2d69826023f60afb219c520

deepmind/open_spiel,deepmind/open_spiel,deepmind/open_spiel,deepmind/open_spiel,deepmind/open_spiel,deepmind/open_spiel