New review comment by kawaiiamber on void-packages repository

https://github.com/void-linux/void-packages/pull/27855#discussion_r567166327

Comment:
Line 49 of their Makefile uses `which` to check for pkg-config, which needs to be added in cross build:
```
if [ "${CROSS_BUILD}" ]; then
	hostmakedepends+=" which"
fi
```
This fixes one error when I tested on aarch64-musl, but other error occurs that I'm still working out.