build: Support bitbake

LDFLAGS can be defined from outside

This will fix observed issues:

    Subprocess output:arm-poky-linux-musleabi-strip:
    /.../demo: file format not recognized

    ERROR: lvgl-0.0.0-r012 do_package_qa:
    QA Issue: File /usr/lib/lvgl/bin/demo in package lvgl
    doesn't have GNU_HASH (didn't pass LDFLAGS?) [ldflags]

Relate-to: lvgl/lvgl#2534
Signed-off-by: Philippe Coval <[email protected]>

Makefile

@@ -6,7 +6,7 @@
 MAKEFLAGS 			:= -j $(shell nproc)
 SRC_EXT      		:= c
 OBJ_EXT				:= o
-CC 					:= gcc
+CC 					?= gcc
 
 SRC_DIR				:= ./
 WORKING_DIR			:= ./build
@@ -29,7 +29,7 @@ DEFINES				:= -D SIMULATOR=1 -D LV_BUILD_TEST=0
 
 # Include simulator inc folder first so lv_conf.h from custom UI can be used instead
 INC 				:= -I./ui/simulator/inc/ -I./ -I./lvgl/
-LDFLAGS 			:= -lSDL2 -lm
+LDLIBS	 			:= -lSDL2 -lm
 BIN 				:= $(BIN_DIR)/demo
 
 COMPILE				= $(CC) $(CFLAGS) $(INC) $(DEFINES)
@@ -47,7 +47,7 @@ $(BUILD_DIR)/%.$(OBJ_EXT): $(SRC_DIR)/%.$(SRC_EXT)
 
 default: $(OBJECTS)
 	@mkdir -p $(BIN_DIR)
-	$(CC) -o $(BIN) $(OBJECTS) $(LDFLAGS)
+	$(CC) -o $(BIN) $(OBJECTS) $(LDFLAGS) ${LDLIBS}
 
 clean:
 	rm -rf $(WORKING_DIR)