If I download its source code:

$ cd abslibre/libre/retroarch
$ makepkg -o

Then it unpacks the source code in src/RetroArch/

And in media/icons/LICENSE/, we have the license of media/icons which states that (in LICENSE.txt):

License
=======

Icons generated with the Android Material Icon Generator are licensed under the Creative Commons Attribution-NonCommercial 3.0 License (https://creativecommons.org/licenses/by-nc/3.0/).

For commercial usage, please submit a request under https://goo.gl/forms/zX8GZ3Jz89SRyHdJ2 or send us an email to material-icons@bitdroid.de.

Google Material Icons License
=============================

This license applies to the Google Material Icons, which can be seen on the front page of the Android Material icon generator.

(Copied from https://github.com/google/material-design-icons)
We have made these icons available for you to incorporate them into your
products under the Creative Common Attribution 4.0 International License (CC-BY
4.0, https://creativecommons.org/licenses/by/4.0/). Feel free to remix and
re-share these icons and documentation in your products.  We'd love attribution
in your app's *about* screen, but it's not required.  The only thing we ask is
that you not re-sell the icons themselves.