flx: require cl-lib; avoid ugly eval-when-compile

It just requires one small change: replace loop with cl-loop everywhere.

Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com>
flx-ido: don't require cl; flx requires it anyway

Also s/loop/cl-loop/ like in flx.

Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com>