[logging] always set up logging on startup

Summary: Avoid polluting stdout and stderr for executables that are always supposed to log into files.

Reviewed By: dulmarod

Differential Revision: D4008888

fbshipit-source-id: 1366498

infer/src/base/Logging.ml

@@ -76,6 +76,9 @@ let set_log_file_identifier string_opt =
     err_formatter := err_fmt;
   )
 
+(* set up log files on startup if needed *)
+let () = set_log_file_identifier None
+
 let log_file_names () = (!out_file, !err_file)
 
 (** type of printable elements *)