test: add phpx directory detection test

test_phpx_dir.php

@@ -0,0 +1,12 @@
+<?php
+
+require __DIR__ . '/vendor/autoload.php';
+
+$compiler = new PhpAot\Php\CompilerBase();
+$ref = new ReflectionMethod($compiler, 'getPhpxDir');
+$ref->setAccessible(true);
+
+echo "Testing getPhpxDir()...\n";
+echo "PHPX_HOME env: " . (getenv('PHPX_HOME') ?: '(not set)') . "\n";
+echo "Result: " . $ref->invoke($compiler) . "\n";
+echo "Directory exists: " . (is_dir($ref->invoke($compiler)) ? 'YES' : 'NO') . "\n";