allocating more than 2GB memory is slow.

Zend/tests/bug55509.phpt

@@ -5,6 +5,7 @@ Bug #55509 (segfault on x86_64 using more than 2G memory)
 if (PHP_INT_SIZE == 4) {
   die('skip Not for 32-bits OS');
 }
+if (getenv("SKIP_SLOW_TESTS")) die("skip slow test");
 // check the available memory
 if (PHP_OS == 'Linux') {
   $lines = file('/proc/meminfo');