New review comment by Logarithmus on void-packages repository

https://github.com/void-linux/void-packages/pull/31811#discussion_r675990723

Comment:
> This is incorrect. `ninja` will run in parallel by default. I would rather change `makejobs` in `common/xbps-src/libexec/xbps-src-docheck.sh`

Sorry, but I can't find `makejobs` in `common/xbps-src/libexec/xbps-src-docheck.sh`. Where should I define it?