The WiredTiger project uses autoconf to generate header files that enable and disable some functionality. Since MongoDB uses scons the MongoDB tree contains pre-generated versions of those files.

When a new variable is added that appears in wiredtiger_config.h the MongoDB files will be out of date, and there is no mechanism in place to monitor when they are out of date.

The particular files are (currently):
https://github.com/mongodb/mongo/tree/master/src/third_party/wiredtiger/build_darwin
https://github.com/mongodb/mongo/tree/master/src/third_party/wiredtiger/build_freebsd
https://github.com/mongodb/mongo/tree/master/src/third_party/wiredtiger/build_linux
https://github.com/mongodb/mongo/tree/master/src/third_party/wiredtiger/build_openbsd
https://github.com/mongodb/mongo/tree/master/src/third_party/wiredtiger/build_solaris