New review comment by not-chicken on void-packages repository

https://github.com/void-linux/void-packages/pull/27996#discussion_r560250166

Comment:
Replace these with:
```
configure_args+=" -Dheader_path=${XBPS_CROSS_BASE}/opt/vc/include/IL"
```
and keep `$(vopt_if rpi -Dtarget=rpi -Dtarget=generic)` in `configure_args`. This may fix rpi target.