round() with a RoundingMode enum aborts the compiled binary with stack smashing

[Giandonn]

Summary

genRound sends the third argument of round() through convertIntExpr.
Since PHP 8.4 that parameter is a RoundingMode enum, and php::fn::round()
declares the mode as an Int, so the enum is put through an object-to-int
conversion.

Reproducer

<?php
function main(): void
{
    echo "round(2.5,0,HalfEven): ", round(2.5, 0, RoundingMode::HalfEven), "\n";
}

Expected (PHP 8.5.4)

round(2.5,0,HalfEven): 2

Actual (compiled binary)

*** stack smashing detected ***: terminated
Aborted

What is actually going on

Two separate problems stack on this one line, and they are worth separating:

1. phpx returns an unevaluated class constant for an enum case of an
   internal class, so RoundingMode::HalfEven is not a usable value at all.
   That is the crash. Reported as constant(zend_class_entry*, name) returns an unevaluated class constant phpx#97, with a fix in fix: evaluate class constants before returning them phpx#98.

2. This repo converts that argument to an int. With the phpx side fixed, the
   compiled binary stops crashing but still disagrees with PHP:

   Warning: Object of class RoundingMode could not be converted to int
   3
   

   The conversion yields 1, which is PHP_ROUND_HALF_UP, so banker's rounding
   silently becomes half away from zero.

Measured on a compiled binary, PHP 8.5.4 ZTS + embed, GCC 15, Linux x64:

phpx	genRound	round(2.5, 0, RoundingMode::HalfEven)
master	master	stack smashing abort
fixed	master	warning, then 3
master	fixed	clean TypeError, no memory corruption
fixed	fixed	2, same as PHP

Code that spells out HalfEven is usually money code, where half-up is the
exact behaviour it was avoiding.

Suggested fix

Let a mode that is not statically an int fall through to the dynamic path, which
passes the enum to the runtime function unchanged. The legacy PHP_ROUND_*
integer constants keep the native call. PR follows.