Add simple hello-world example package

Config.in

@@ -0,0 +1 @@
+source "$BR2_EXTERNAL_buildroot_playground_PATH/package/helloworld/Config.in"

external.mk

@@ -0,0 +1 @@
+include $(BR2_EXTERNAL_buildroot_playground_PATH)/package/*/*.mk

output/.config

@@ -3802,3 +3802,4 @@ BR2_LINUX_KERNEL_CUSTOM_GIT_VERSION=""
 # my playground for buildroot, currently on a raspberry pi (in /home/laurens/projects/buildroot_playground)
 #
 BR2_EXTERNAL_buildroot_playground_PATH="/home/laurens/projects/buildroot_playground"
+BR2_PACKAGE_HELLOWORLD=y

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)