In pg_upgrade, report errno string if file existence check returns an

error and errno != ENOENT.

contrib/pg_upgrade/relfilenode.c

@@ -205,8 +205,9 @@ transfer_relfile(pageCnvCtx *pageConverter, FileNameMap *map,
 				if (errno == ENOENT)
 					return;
 				else
-					pg_log(PG_FATAL, "non-existant file error while copying relation \"%s.%s\" (\"%s\" to \"%s\")\n",
-						   map->nspname, map->relname, old_file, new_file);
+					pg_log(PG_FATAL, "error while checking for file existance \"%s.%s\" (\"%s\" to \"%s\"): %s\n",
+						   map->nspname, map->relname, old_file, new_file,
+						   getErrorText(errno));
 			}
 			close(fd);
 		}