Avoid potential lifetime issues with temporary std::wstring objects. * sysdep.cc (F__open_with_system_app__, get_regkey_value, get_regkey_names), file-ops.cc (rename), lo-sysdep.cc (get_dirlist, fopen, getenv_wrapper), oct-shlib.cc (octave_w32_shlib): Explicitly create std::wstring object with well-defined lifetime when passing the pointer to the underlying c_str to a function.

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