Description:
------------
We started testing a large codebase in 7.1.0RC3 and found a segfault, reduced to the testcase below. It does NOT segfault in a debug-build.

Test script:
---------------
<?php

class AAAAAAAAAAAAAA
{
        public function __get($name)
        {
                throw new React_UnknownEntryException;
        }
}

function g($class) {
        eval('class ' . $class . ' extends React_Exception {}');
        
        return true;
}

class React_Exception extends Exception
{
        public function __toString()
        {        
                try
                {
                        $registry = new AAAAAAAAAAAAAA;
                        return $registry->Translate->getTranslation('waa');
                }
                catch (Throwable $e)
                {
                        // ignore
                }
        }
}

class NoClone {
        public function __clone() {
                throw new React_CloneException;
        }
}

class UUUUUUUUUUUUUUUUUU
{
        public function __get($name)
        {
                return new NoClone;
        }
}

class Test
{
        public function testClone()
        {
                $u = new UUUUUUUUUUUUUUUUUU;
                $b = clone $u->x;
        }
}

spl_autoload_unregister('spl_autoload');
spl_autoload_register('g');
$t = new Test;
$t->testClone();

Expected result:
----------------
Warning: React_CloneException::__toString() must return a string in Unknown on line 0

Fatal error: Uncaught 
  thrown in test.php on line 35


Actual result:
--------------
Program received signal SIGSEGV, Segmentation fault.
0x0000000000657540 in _emalloc ()
(gdb) bt
#0  0x0000000000657540 in _emalloc ()
#1  0x0000000000672344 in zend_string_tolower ()
#2  0x0000000000659f59 in ?? ()
#3  0x00000000006668e4 in ?? ()
#4  0x0000000000667078 in ?? ()
#5  0x000000000066967a in ?? ()
#6  0x00000000006696cf in ?? ()
#7  0x0000000000641b82 in ?? ()
#8  0x0000000000643698 in compile_string ()
#9  0x00000000006dc77e in ?? ()
#10 0x0000000000715ed3 in ?? ()
#11 0x00000000006c230b in execute_ex ()
#12 0x000000000066cb41 in zend_call_function ()
#13 0x0000000000697fab in zend_call_method ()
#14 0x0000000000559bfc in ?? ()
#15 0x000000000066c9f7 in zend_call_function ()
#16 0x000000000066cf85 in zend_lookup_class_ex ()
#17 0x000000000066d898 in zend_fetch_class_by_name ()
#18 0x0000000000716c97 in ?? ()
#19 0x00000000006c230b in execute_ex ()
#20 0x000000000066cb41 in zend_call_function ()
#21 0x0000000000697fab in zend_call_method ()
#22 0x00000000006b2d9a in ?? ()
#23 0x00000000006b48b2 in ?? ()
#24 0x00000000006f300c in ?? ()
#25 0x00000000006c230b in execute_ex ()
#26 0x000000000066cb41 in zend_call_function ()
#27 0x0000000000697fab in zend_call_method ()
#28 0x00000000004318a0 in zend_exception_error ()
#29 0x000000000067b40c in zend_execute_scripts ()
#30 0x000000000061bbab in php_execute_script ()
#31 0x000000000071daac in ?? ()
#32 0x0000000000433a2f in ?? ()
#33 0x00007ffff6219291 in __libc_start_main () from /usr/lib/libc.so.6
#34 0x0000000000433b6a in _start ()