[texhax] Superscript ordinal indicators in dates?

[Joel C. Salomon]

How can I get the date in my LaTeX article to display the ordinal
indicator in superscript?  E.g., July 4<sup>th</sup>, 1776

I’m using XeLaTeX, so I can manually get the effect I want via “July
4\textsuperscript{th}, 1776”; I’d like to know how to get the effect
automatically.

Thanks,
—Joel Salomon