New review comment by Logarithmus on void-packages repository

https://github.com/void-linux/void-packages/pull/26339#discussion_r602527290

Comment:
@ericonr me too, but I've tried different options without much luck.
See https://github.com/void-linux/void-packages/pull/26339#issuecomment-730720567 and other comments in this PR for more context.
I've created `_libtool` variable to avoid duplication.