Move .elf file to it's own target

Makefile.include

@@ -65,15 +65,7 @@ BASELIBS += $(USEPKG:%=${BINDIR}%.a)
 .PHONY: all clean flash doc term objsize buildsize buildsizes buildsizes-diff
 
 ## make script for your application. Build RIOT-base here!
-all: $(BINDIR)$(PROJECT).a
-	@echo "Building application $(PROJECT) for $(BOARD) w/ MCU $(MCU)."
-	"$(MAKE)" -C $(RIOTBOARD)/$(BOARD)
-	"$(MAKE)" -C $(RIOTBASE)
-ifeq ($(BUILDOSXNATIVE),1)
-	$(AD)$(LINK) $(UNDEF) -o $(BINDIR)$(PROJECT).elf $(BASELIBS) $(LINKFLAGS) -Wl,-no_pie
-else
-	$(AD)$(LINK) $(UNDEF) -o $(BINDIR)$(PROJECT).elf -Wl,--start-group $(BASELIBS) -lm -Wl,--end-group  -Wl,-Map=$(BINDIR)$(PROJECT).map $(LINKFLAGS)
-endif
+all: $(BINDIR)$(PROJECT).elf
 	$(AD)$(SIZE) $(BINDIR)$(PROJECT).elf
 	$(AD)$(OBJCOPY) $(OFLAGS) $(BINDIR)$(PROJECT).elf $(BINDIR)$(PROJECT).hex
 
@@ -88,6 +80,16 @@ SRC = $(wildcard *.c)
 # string array of all names replaced .c with .o
 OBJ = $(SRC:%.c=${BINDIR}${PROJECT}/%.o)
 
+$(BINDIR)$(PROJECT).elf: $(BINDIR)$(PROJECT).a
+	@echo "Building application $(PROJECT) for $(BOARD) w/ MCU $(MCU)."
+	"$(MAKE)" -C $(RIOTBOARD)/$(BOARD)
+	"$(MAKE)" -C $(RIOTBASE)
+ifeq ($(BUILDOSXNATIVE),1)
+	$(AD)$(LINK) $(UNDEF) -o $@ $(BASELIBS) $(LINKFLAGS) -Wl,-no_pie
+else
+	$(AD)$(LINK) $(UNDEF) -o $@ -Wl,--start-group $(BASELIBS) -lm -Wl,--end-group  -Wl,-Map=$(BINDIR)$(PROJECT).map $(LINKFLAGS)
+endif
+
 $(BINDIR)$(PROJECT).a: $(OBJ)
 	$(AD)$(AR) -rc $(BINDIR)$(PROJECT).a $(OBJ)