userspace: Add empty libm and libpthread

These making porting stuff easier. I could not find a way to tell CMake
that the system does not have threads library

userspace/libraries/CMakeLists.txt

@@ -5,6 +5,8 @@ set(USERSPACE_LIBRARIES
 	LibGUI
 	LibImage
 	LibInput
+	LibMath
+	LibPthread
 )
 
 foreach(library ${USERSPACE_LIBRARIES})