add -aui/-naui flags for allowing undecidable instances

This MR adds the -aui and -naui flags to enable or disable the allowance of undecidable instances (required for some functional dependency trickery such as type arithmetic and type level lists).

The aui flag can be found here: https://gitlab.com/clean-and-itasks/base/compiler/-/blob/main/main/compile.icl#L218