fix platform specific builds

rai/lib/utility.hpp

@@ -1,6 +1,7 @@
 #pragma once
 
 #include <functional>
+#include <mutex>
 #include <thread>
 #include <vector>
 

rai/plat/linux/priority.cpp

@@ -1,4 +1,4 @@
-#include <rai/utility.cpp>
+#include <rai/lib/utility.hpp>
 
 #include <pthread.h>
 
@@ -13,4 +13,4 @@ void rai::work_thread_reprioritize ()
 		auto result (pthread_setschedparam (handle, policy, &sched));
 		(void) result;
 	}
-}
+}

rai/plat/windows/priority.cpp

@@ -1,8 +1,8 @@
-#include <rai/utility.hpp>
+#include <rai/lib/utility.hpp>
 
 #include <windows.h>
 
 void rai::work_thread_reprioritize ()
 {
 	auto SUCCESS (SetThreadPriority (GetCurrentThread(), THREAD_MODE_BACKGROUND_BEGIN));
-}
+}