New review comment by ericonr on void-packages repository

https://github.com/void-linux/void-packages/pull/28948#discussion_r579729526

Comment:
```suggestion
post_install() {
	vinstall mcpp_lib.h 644 usr/include
	vinstall mcpp_out.h 644 usr/include
	vlicense LICENSE
}
```

This is a nitpick, so you don't need to apply it. But I think this works. And from what I looked at the Makefile, you only really need to set `LIBDIR` if you're using `make install`.