Avoid double-declaration of ARRAY_SIZE

for external ioengines. ARRAY_SIZE is a very common
declaration - e.g. Ceph is using this as well.

Signed-off-by: Daniel Gollub <daniel.gollub@gmail.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/fio.h b/fio.h
index ed034cb..4d4af0a 100644
--- a/fio.h
+++ b/fio.h
@@ -618,7 +618,9 @@
 extern const char *fio_get_arch_string(int);
 extern const char *fio_get_os_string(int);
 
+#ifdef FIO_INTERNAL
 #define ARRAY_SIZE(x) (sizeof((x)) / (sizeof((x)[0])))
+#endif
 
 enum {
 	FIO_OUTPUT_TERSE	= 0,