New review comment by ahesford on void-packages repository

https://github.com/void-linux/void-packages/pull/23613#discussion_r456619113

Comment:
Define a `pre_build` function here:
```
pre_build() {
	cat <<-EOF > setup.cfg
	[libs]
	system_freetype = true
	system_qhull = true
	EOF
}
```
The build failures occur when trying to build an in-tree copy of `freetype`, but we can just link to the version shipped with Void. While we're at it, we might as well link to `libqhull` that's provided by Void.