Makefile: rename MAKEFILES -> BUILD_CONFIGURATION

MAKEFILES is special and automatically inherited in sub makes.

Makefile

@@ -672,15 +672,15 @@ DEP := $(patsubst %.o, %.d, $(OBJ))
 # will result in the rebuild.
 -include ${DEP}
 
-MAKEFILES :=  Makefile $(BUILD_TOP)/Config.make
-$(OBJDIR)/%.o : %.cu $(MAKEFILES)
+BUILD_CONFIGURATION := Makefile $(BUILD_TOP)/Config.make
 
+$(OBJDIR)/%.o : %.cu $(BUILD_CONFIGURATION)
 	@echo $(SEPARATOR)
 	@echo creating $@ for $(ARCH) with build type $(BUILDTYPE)
 	@mkdir -p $(dir $@)
 	$(NVCC) -c $< -o $@ $(COMMON_FLAGS) $(CUFLAGS) $(INCLUDEPATH:%=-I%) -Xcompiler "-fPIC -Werror"
 
-$(OBJDIR)/%.o : %.cpp $(MAKEFILES)
+$(OBJDIR)/%.o : %.cpp $(BUILD_CONFIGURATION)
 	@echo $(SEPARATOR)
 	@echo creating $@ for $(ARCH) with build type $(BUILDTYPE)
 	@mkdir -p $(dir $@)