make windows-compliant

- fix BS_thread_pool include error (pulls in windows.h, symbols were
redefined)
- remove all std::println uses :(, seems like mingw doesn't like those
- allow to disable backward from cmake

src/physics.cpp

@@ -10,11 +10,6 @@
 #include <utility>
 #include <vector>
 
-#ifdef THREADPOOL
-#define BS_THREAD_POOL_NATIVE_EXTENSIONS
-#include <BS_thread_pool.hpp>
-#endif
-
 #ifdef TRACY
 #include "tracy.hpp"
 #include <tracy/Tracy.hpp>