utfebcdic.h: Comment changes only

Clarifications and typo fix.
Fatalize splitting '(?' and '(*' in regexes

Inserting spaces or comments between the '(' and '?' or '*' has been
deprecated since v5.18.0.
charnames: Eliminate need to sync code in two places

This refactors the code so that it doesn't have to be kept in sync
with other code.