Description:
------------
If user error handler returns false on amd64, PHP crashes. This is due to the fact that zend_error uses va_list twice, which does not work on systems where va_arg modifies va_list. 

Reproduce code:
---------------
<?
                                                                                                    
function my_error($errno, $errstr, $errfile, $errline)
{
        print "$errstr ($errno) in $errfile:$errline\n";
        return false;
}
                                                                                                    
set_error_handler('my_error');
                                                                                                    
$f = fopen("/tmp/blah", "r");
?>