If we create an off_t type, define SIZEOF_OFF_T.

rsync.h

@@ -465,6 +465,8 @@ typedef unsigned int mode_t;
 #endif
 #ifndef HAVE_OFF_T
 typedef long off_t;
+#undef SIZEOF_OFF_T
+#define SIZEOF_OFF_T SIZEOF_LONG
 #endif
 #ifndef HAVE_SIZE_T
 typedef unsigned int size_t;