Skip test on big-endian architectures

Due to the memory layout on BE architectures, the address would be
`0x2a00000000` instead of `0x2a` on little-endian architectures.

Author: cmb69

ext/ffi/tests/bug79571.phpt

@@ -3,6 +3,9 @@ Bug #79571 (FFI: var_dumping unions may segfault)
 --SKIPIF--
 <?php
 if (!extension_loaded('ffi')) die('skip ffi extension not available');
+if (pack('S', 0xABCD) !== pack('v', 0xABCD)) {
+    die('skip for little-endian architectures only');
+}
 ?>
 --FILE--
 <?php