New review comment by sgn on void-packages repository

https://github.com/void-linux/void-packages/pull/27590#discussion_r552533516

Comment:
Sorry but I couldn't follow. `/proc/<pid>/mem` is available on all our targets.
I think the correct approach would be add an `AC_CACHE_CHECK` for some value instead https://www.gnu.org/software/autoconf/manual/autoconf-2.67/html_node/Caching-Results.html