Migrate skip checks to --EXTENSIONS--, p3

For rationale, see #6787

Extensions migrated in part 3:
* ftp
* gmp
* iconv
* opcache
* shmop

Fix #79475: [JIT] func_get_args() assertion violation

`func_get_args()` may return `zend_empty_array`, which has refcount 2
to enforce separation. We have to cater to that during type

Fix #79475: [JIT] func_get_args() assertion violation

`func_get_args()` may return `zend_empty_array`, which has refcount 2
to enforce separation. We have to cater to that during type inference
so that the optimization in the JIT macro `SEPARATE_ARRAY` doesn't
prevent the separation.

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