ext/opcache/ZendAccelerator.c: Restrict MD5 header include to Windows

As it is only ever used in accel_gen_uname_id() which is Windows only

Author: Girgias

ext/opcache/ZendAccelerator.c

@@ -47,10 +47,10 @@
 #include "zend_accelerator_hash.h"
 #include "zend_file_cache.h"
 #include "ext/pcre/php_pcre.h"
-#include "ext/standard/md5.h"
 
 #ifdef ZEND_WIN32
 # include "ext/hash/php_hash.h"
+# include "ext/standard/md5.h"
 #endif
 
 #ifdef HAVE_JIT