The backport of SERVER-39004 to v4.0 introduced a msg to stdout when starting mongod that logs the value of wiredTigerMaxCacheOverflowFileSizeGB setting even when set to its default value of 0.

alexc@kitty:~/work/mongo$ ./mongod --logpath=data/mongod.log --dbpath=data/ --fork
2019-08-14T00:33:16.654+0000 I STORAGE  [main] Max cache overflow file size custom option: 0
about to fork child process, waiting until server is ready for connections.
forked process: 27798
child process started successfully, parent exiting

A normal invocation of mongod shouldn't be causing the setting to be written to stdout like this. It'd be acceptable to only print it when explicitly set (like the wiredTigerEngineConfig option) or to just not print it at all.