move reference to pcre.h out of spl_iterators.h

[Danack]

Description

Currently spl_iterators.h includes php_pcre.h so that it can be reference in the spl_dual_it_object struct but only as a pointer to a .

This makes a dependency on the pcre2.h file for extensions that include the spl_iterators.h. Apparently this causes problems for people installing extensions that include spl_iteterators header, presumably due to the common swapping out of PCRE bundled vs system?

Would it be possible to make the header not depend on the php_pcre.h file, either through moving the relevant parts to a spl-private file or using an void pointer?

btw feel free to close if this is non-trivial. I'd missed the fact that as the countable_ce was moved from spl to zend, I no longer need to include the spl header anyway....

[nikic]

Using a forward declare would be enough, but in this case moving the structure definition out of the header seems best, it should not be public.