Revert "[conf] remove duplicates after setting all flags and sources"

Doesn't work as intended (yet).
The sorting e.g. splits up `pkg-config glib-2.0 --cflags` into
--cflags` glib-2.0 `pkg-config
so it doesn't work anymore...
One way could be to make sure to resolve these first before sorting.

This reverts commit 70168207ab.

sw/airborne/Makefile

@@ -33,8 +33,6 @@ ifneq ($(MAKECMDGOALS),clean)
   include $(PAPARAZZI_HOME)/var/$(AIRCRAFT)/Makefile.ac
   $(TARGET).srcs += $($(TARGET).EXTRA_SRCS)
   include ../../conf/Makefile.local
-	$(TARGET).CFLAGS := $(sort $($(TARGET).CFLAGS))
-	$(TARGET).srcs := $(sort $($(TARGET).srcs))
 
 # check if ARCHDIR is set
   ifeq ($($(TARGET).ARCHDIR), )

sw/tools/gen_aircraft.ml

@@ -87,7 +87,7 @@ let dump_module_section = fun xml f ->
   List.iter (fun target -> fprintf f "%s.CFLAGS += -I modules -I arch/$(ARCH)/modules\n" target) target_list;
 **)
   (** include modules directory for ALL targets and not just the defined ones **)
-  fprintf f "$(TARGET).CFLAGS += -Imodules -Iarch/$(ARCH)/modules\n";
+  fprintf f "$(TARGET).CFLAGS += -I modules -I arch/$(ARCH)/modules\n";
   List.iter (fun dir -> let dir_name = (String.uppercase dir)^"_DIR" in fprintf f "%s = modules/%s\n" dir_name dir) dir_list;
   (* parse each module *)
   List.iter (fun m ->