[RFC] Autoloading functions

[withinboredom]

This PR implements the function autoload v4 RFC.

Key overview:

1. An additional parameter is added to spl_autoload_register to allow registering functions to load functions and/or classes. This involves two new constants: SPL_AUTOLOAD_CLASS and SPL_AUTOLOAD_FUNCTION.
2. Significant changes to zend_execute.c and zend_execute.h to implement autoloading of functions.
3. The addition of a new helper function: zend_locate_function which searches the function table before performing an autoload. It returns the zval of the function, or NULL. It can be used as a drop-in replacement for looking up a function in the function table directly.
4. Additional changes to the SPL library, as documented in the RFC.
5. New tests that ensure the RFC is implemented correctly.

Note before merging: Symfony has some code that is broken by this change. I've updated the benchmark loader to point to my fork of the benchmarks. As you can see the changes are very minimal.

Note: this does not include potential changes to opcache's JIT, which may need changes in zend_jit_find_func_helper, zend_jit_jmp_frameless_helper, and zend_jit_find_ns_func_helper

[withinboredom]

I do not have an ARM machine to test this PR on. Can someone potentially get the logs for the failing tests?

[iluuu1994]

Possibly, the job isn't failing because of arm, but because of the test flags. Namely:

  -d opcache.enable_cli=1 \
  -d opcache.jit_buffer_size=64M \
  -d opcache.jit=tracing \
  -d zend_test.observer.enabled=1 \
  -d zend_test.observer.show_output=0 \
  --repeat 2

[withinboredom]

@iluuu1994, looks like a bug with opcache?

The error is:

Fatal error: Namespace declaration statement has to be the very first statement or after any declare call in the script

and the script is:

namespace {
    spl_autoload_register(function(string $name, int $mode) {
        echo "name=$name, mode=$mode\n";
    }, true, false, SPL_AUTOLOAD_FUNCTION);
}

namespace Foo {
    echo strlen('foo') . "\n";
}