[Bug libstdc++/71500] regex::icase only works on first character in a range

[mwd at cert dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71500

--- Comment #5 from mwd at cert dot org ---
All of the ECMAScript engines I have found work with this , and the ECMAScript
specs seem to imply that this should work as well.