New comment by tornaria on void-packages repository

https://github.com/void-linux/void-packages/pull/45735#issuecomment-1690751328

Comment:
Note all the added patch does is moving the definition of `inline float fgamma()` verbatim from `first.h` to `usual.cc` which is the only place where it is used.

In the template I added a simple test in `post_install()` that compiles `#include <giac/giac.h>` to make sure it works.