Description:
------------
in php_error_cb:

freeing PG(last_error_message) and PG(last_error_file) without blocking alarm 
signal.

so there is a chance that php will segfault when max_execution_time limit 
reachead.

since zend_signal was introduced in PHP 5.4,  so I think it's okey to add signal 
block mechanism for this codes.

Test script:
---------------
<?php
error_reporting(E_ALL|E_NOTICE);
set_time_limit(1);

while(1) {   
    $a = $arr['index_miss'];
}
?>

do following steps:
1. gdb php 
2. b php_error_cb
3. r "above script"
4. when breakpoint reach: 
   893			if (PG(last_error_message)) {
   (gdb) 
   894				free(PG(last_error_message));
5. signal SIGPROF
6. next (*n)
*** glibc detected *** double free or corruption (fasttop): 0x0000000001207ca0 ***

Expected result:
----------------
no segfault

Actual result:
--------------
segfault