Add simple hello-world example package

package/helloworld/Config.in

@@ -0,0 +1,4 @@
+config BR2_PACKAGE_HELLOWORLD
+       bool "helloworld-app"
+       help
+        A classic C hello-world application

package/helloworld/helloworld.mk

@@ -0,0 +1,13 @@
+HELLOWORLD_VERSION = v1.0
+HELLOWORLD_SITE = $(TOPDIR)/../package/helloworld/src
+HELLOWORLD_SITE_METHOD = local
+
+define HELLOWORLD_BUILD_CMDS
+	$(TARGET_MAKE_ENV) CC=arm-buildroot-linux-uclibcgnueabihf-gcc $(MAKE) -C $(@D)
+endef
+
+define HELLOWORLD_INSTALL_TARGET_CMDS
+	rsync -a $(@D) $(TARGET_DIR)/root/
+endef
+
+$(eval $(generic-package))

package/helloworld/src/main.c

@@ -0,0 +1,7 @@
+#include <stdio.h>
+
+int main(void) {
+    printf("Hello World!\n");
+
+    return 0;
+}

package/helloworld/src/makefile

@@ -0,0 +1,6 @@
+APP_NAME=main
+
+$(APP_NAME):
+
+clean:
+	rm -rf $(APP_NAME)