New review comment by paper42 on void-packages repository

https://github.com/void-linux/void-packages/pull/34651#discussion_r773476244

Comment:
```suggestion
	make CXX="$CXX" LD="$LD" STRIP=: -f makefile
	make CXX="$CXX" LD="$LD" STRIP=: -f makefile lib
```
Then we should be able to just vinstall from `$wrksrc`. We won't need `cp -a . ../libunrar` in post_install which is a bit problematic because `./xbps-src clean unrar` won't remove it.