Previously, FEX would use `$HOME/.fex-emu` for its data and config if
`XDG_CONFIG_HOME` and/or `XDG_DATA_HOME` were unset. This doesn't follow
XDG, so instead we do a fallback to `$HOME/.config` and
`$HOME/.local/share` respectively if XDG env vars are unset. Also,
pre-emptively creates those directories since `~/.local/share` and
`~/.config` existing is technically not a guarantee if XDG dirs are unset.
Signed-off-by: crueter <crueter@eden-emu.dev>