[admin] Use GitHub action to attach bins to PRs

[JoeMatt]

This core is very fast to compile and has nearly no dependencies so it's super easy and fast to compile for multiple platforms.

To speed up PR reviews, I propose having a GitHub action to compile the most common platform libs from source on PR open so users can easily copy the binary to their Retroarch install and test that PR's code without having to know how to clone and build locally.

The GitHub action can attach the binaries as a action generated resource without needing to use external hosting since they're small in size.

[hizzlekizzle]

I think that's a great idea.