regexec.c: Latin1 chars can fold match UTF8_ALL

regexec.c: Latin1 chars can fold match UTF8_ALL

Some ANYOF regnodes have the ANYOF_UNICODE_ALL flag set, which means
they match any non-Latin1 character.  These should match /i (in a utf8
target string) any ASCII or Latin1 character that folds outside the
Latin1 range

As part of this patch, an internal only macro is renamed to account for its
new use in regexec.c.  The cumbersome name is to ward off others from
using it until the final semantics have been settled on.