Zend: add const qualifiers to the majority of compare functions

[Girgias]

This sadly does not include zend_compare() and functions relying on it due to 2 reasons:

• The compare object handler doesn't take const pointers
• The cast object handler (used for comparisons against other types) doesn't take const pointers

[TimWolla]

• The compare object handler doesn't take const pointers

• The cast object handler (used for comparisons against other types) doesn't take const pointers

Can this be changed or are there implementations that require the parameter to be non-const? Fixing this in external extensions should be a simple #if.

[Girgias]

• The compare object handler doesn't take const pointers
• The cast object handler (used for comparisons against other types) doesn't take const pointers

Can this be changed or are there implementations that require the parameter to be non-const? Fixing this in external extensions should be a simple #if.

The default compare hook (zend_std_compare_objects()) relies on zend_compare(), and adds recursion protections to OP1 so it seems difficult to make the parameters const.