Include the most specific header documented by MSDN instead.

Just like std::condition_variable, which however has no way to specify
the std::mutex directly.

Make sure this deprecated API is not used.

Use CRITICAL_SECTION and CONDITION_VARIABLE.  This requires Windows
Vista or newer.  It fixes problems with GLib threading objects that
were implicitly created by static constructors before g_thread_init().

Use a custom pthread_mutex_t wrapper because std::mutex adds overhead.