While we already have a test for `p_regexec` with `LC_CTYPE` being
modified, `regexec` also alters behavior as soon as `LC_COLLATE` is
being modified. Most importantly, `LC_COLLATE` changes the way how
ranges are interpreted to just not handling them at all. Thus, ensure
that either we use `regcomp_l` to avoid this, or that we've fallen back
to our builtin regex functionality which also behaves properly.