${CUSTOMFILES} is often used to produce dependencies for the build, so it needs to be first.

src/actions/make/make_cpp.lua

@@ -352,7 +352,7 @@
 
 
 	function make.cppTargetRules(prj)
-		_p('$(TARGET): $(GCH) $(OBJECTS) $(LDDEPS) $(RESOURCES) ${CUSTOMFILES}')
+		_p('$(TARGET): $(GCH) ${CUSTOMFILES} $(OBJECTS) $(LDDEPS) $(RESOURCES)')
 		_p('\t@echo Linking %s', prj.name)
 		_p('\t$(SILENT) $(LINKCMD)')
 		_p('\t$(POSTBUILDCMDS)')