New review comment by paper42 on void-packages repository

https://github.com/void-linux/void-packages/pull/34651#discussion_r773482135

Comment:
hmm, I now see why you did it this way, but this could be better:
```sh
do_build() {
	vsed -e 's/^\(CXXFLAGS\)=\(.*\)/\1+=\2/' \
		 -e 's/^\(LDFLAGS\)=\(.*\)/\1+=-lpthread \2/' \
		 -i makefile
	make CXX="$CXX" LD="$LD" STRIP=: -f makefile
	vbin unrar
	make CXX="$CXX" LD="$LD" STRIP=: -f makefile lib
}
do_install() {
	vlicense license.txt LICENSE
}
```