Avoid double declaration of leXX_to_cpu

for external ioengines. leXX_to_cpu 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/os/os.h b/os/os.h
index 98b4532..b8eee66 100644
--- a/os/os.h
+++ b/os/os.h
@@ -200,6 +200,7 @@
 #endif
 #endif /* FIO_HAVE_BYTEORDER_FUNCS */
 
+#ifdef FIO_INTERNAL
 #define le16_to_cpu(val) ({			\
 	__le16_to_cpu(val);			\
 })
@@ -209,6 +210,8 @@
 #define le64_to_cpu(val) ({			\
 	__le64_to_cpu(val);				\
 })
+#endif
+
 #define cpu_to_le16(val) ({			\
 	__cpu_to_le16(val);			\
 })