Where's the alarm widget on my new HTC One m8? I just "upgraded" to a HTC One M8 from a Galaxy S3 and I can't see how to add the alarm home-screen widget. 

On the S3 there's the '2 x 1 Alarm' widget which is great. How do I add this to my M8 please?

Also, is the disappearance of this due to a newer version of Android or is this widget only available on Samsung phones?
As you've suggested, this is a Samsung-only widget. You can easily find equivalents on Google Play if you want one; perhaps you'll even find something you like better than your old Samsung widget.