Use Windows builtin locking and thread ID functions

Property definitions

libevent :: libevent $ Sys :: use_windows_threads
# Use Windows builtin locking and thread ID functions
fun use_windows_threads: Bool `{
#ifdef EVTHREAD_USE_WINDOWS_THREADS_IMPLEMENTED
	return evthread_use_windows_threads();
#else
	return -1;
#endif
`}
lib/libevent/libevent.nit:579,1--586,2