Disable ZEND_RC_MOD_CHECK() while loading shared extension in FPM

This fixes a ZEND_RC_MOD_CHECK() assertion failure when building with
"-DZEND_RC_DEBUG=1 --enable-debug --enable-zts". php_dl() is called after
startup, and manipulates the refcount of persistent strings, which is not
allowed at this point of the lifecycle.

The dl() function disables the ZEND_RC_MOD_CHECK() assertion before calling
php_dl(). This change applies the same workaround in FPM.

Closes GH-18075

Author: arnaud-lb

sapi/fpm/fpm/fpm_php.c

@@ -93,7 +93,21 @@ int fpm_php_apply_defines_ex(struct key_value_s *kv, int mode) /* {{{ */
 	if (!strcmp(name, "extension") && *value) {
 		zval zv;
 		zend_interned_strings_switch_storage(0);
+
+#if ZEND_RC_DEBUG
+		bool orig_rc_debug = zend_rc_debug;
+		/* Loading extensions after php_module_startup() breaks some invariants.
+		 * For instance, it will update the refcount of persistent strings,
+		 * which is normally not allowed at this stage. */
+		zend_rc_debug = false;
+#endif
+
 		php_dl(value, MODULE_PERSISTENT, &zv, 1);
+
+#if ZEND_RC_DEBUG
+		zend_rc_debug = orig_rc_debug;
+#endif
+
 		zend_interned_strings_switch_storage(1);
 		return Z_TYPE(zv) == IS_TRUE ? FPM_PHP_INI_EXTENSION_LOADED : FPM_PHP_INI_EXTENSION_FAILED;
 	}