The issue of non-working cores on newer versions of RetroArch was caused
by the missing core metadata that is available on
libretro/libretro-super repo. This also allows RetroArch to works
properly, for example there is no need to load a core before loading a
content: RetroArch knows each emulator to load depending on the
available emulators and the file extension.
To load the metadata from `/nix/store`, we need to patch the
`retroarch.cfg`. Sadly this file is only updated when needed, for
example, it will update if the path that it is pointing doesn't exist
anymore. However, before this PR it pointed to a file located in the
HOME directory, so if someone used RetroArch before they will probably
have issues while loading the file.
I tried to patch the configuration loader directly but the code is kinda
messy and this seems very prone to breakage (while the `retroarch.cfg`
file seems an stable interface). One better solution will probably be
the introduction of a module that can generate `retroarch.cfg` file
(since retroarch supports loading a config from `/etc/retroarch.cfg`).
But this will come in a future PR.
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