New review comment by ahesford on void-packages repository

https://github.com/void-linux/void-packages/pull/29326#discussion_r592843999

Comment:
The intermediate variable offers no benefit, just `export GITCOMMIT=55c4[...]` here. (If you can't drop the `do_build` custom function as I discuss below, then you might as well just define it outright within `do_build`.