work around Linux futex implementation

Index: rts/System/CMakeLists.txt
--- rts/System/CMakeLists.txt.orig
+++ rts/System/CMakeLists.txt
@@ -140,7 +140,7 @@ set(sources_engine_System_Threading_Mac
 		"${CMAKE_CURRENT_SOURCE_DIR}/Platform/Mac/Signal.cpp"
 	)
 set(sources_engine_System_Threading_Linux
-		"${CMAKE_CURRENT_SOURCE_DIR}/Platform/Linux/Futex.cpp"
+		"${CMAKE_CURRENT_SOURCE_DIR}/Platform/Mac/Signal.cpp"
 		"${CMAKE_CURRENT_SOURCE_DIR}/Platform/Linux/ThreadSupport.cpp"
 	)
 set(sources_engine_System_Threading_Windows
