* It uses stack a lot, limit the recursion depth like
  we used to do for pcre.
* But don't do that for newer pcre2 that uses stack very little
  (and doesn't support limiting recursion depth anyway).
* Fix tests to verify only that deep recursion doesn't crash, but
  ignore results and warnings (which depend on pcre2 version)
* Also different pcre2 versions report different offset in error messages,
  take that into account.