erlc.mk: Use double-colon targets for source files targets

When files are generated, this avoids a warning because the target would
be redefined.

core/erlc.mk

@@ -179,7 +179,7 @@ define makedep.erl
 					({attribute, _, file, {Dep, _}}, Acc) -> AddHd(Dep, Acc);
 					(_, Acc) -> Acc
 				end, [], Forms)),
-				[F, ":", [[" ", D] || D <- Deps], "\n", CompileFirst(Deps)];
+				[F, "::", [[" ", D] || D <- Deps], "\n", CompileFirst(Deps)];
 			{error, enoent} ->
 				[]
 		end
@@ -204,7 +204,7 @@ endef
 ebin/$(PROJECT).app:: $(ERL_FILES) $(CORE_FILES)
 	$(if $(strip $?),$(call compile_erl,$?))
 
-$(sort $(ERL_FILES) $(CORE_FILES)):
+$(sort $(ERL_FILES) $(CORE_FILES))::
 	@touch $@
 endif