There is a new pull request by varsbhat against master on the void-packages repository

https://github.com/varsbhat/void-packages master
https://github.com/void-linux/void-packages/pull/18542

New Package: libstdc++-doc-20140403
Provides Man Pages for the GNU Standard C++ Library . This is not outdated.

A patch file from https://github.com/void-linux/void-packages/pull/18542.patch is attached