PHPC-2420: Compare Int64 instances without casting

[alcaeus]

PHPC-2420

Previously, we deferred to zend_std_compare_objects when comparing a single Int64 instance with a long or double. By default, this will attempt to cast values to long or double, then comparing it. On 32-bit platforms, this cast truncates any value outside of the 32-bit range and yields a warning about this truncation. This means that we were not able to properly compare such values, even when we technically would easily be able to (as only the value of ZEND_LONG is limited to 32 bits, but int64_t is still available).

This PR changes this logic to specifically handle comparisons between to Int64 instances as well as a single Int64 instance with a long or double. Only if the instance is being compared with anything else will we attempt to cast the value. This removes warnings and fixes comparisons of 64-bit values on 32-bit platforms.

[GromNaN]

LGTM as tests shows this is correct.

[alcaeus]

After some more investigation, I remembered that PHP 7.4 still has the old comparison logic, where the compare_objects handler was only used when comparing two objects, while the compare handler handled comparing an object to any other zval (see code). In PHP 8, comparisons were simplified, with the original compare handler being removed and compare_objects renamed to compare.