https://mariadb.com/kb/en/installing-galera-from-source/
The documentation states:

'Newer MariaDB servers include Galera by default.' - this is correct, the code is included.

However, directly under it it lists the >= 10.2 build commands and the cmake command does not have -WITH_WSREP included. This is not correct. If build without this option, the Galera lib will not be build (tested/verified on 10.4.13 build)

The script mentioned just under it (./BUILD/compile-pentium64-wsrep) does have the this option;

/test/MariaDBEnterprise$ cat ./BUILD/compile-pentium64-wsrep | grep with-wsrep

extra_configs="$pentium_configs $static_link $wsrep_configs --with-wsrep"

So the code, but not the manual, is correct. To fix, simply change the line to read:

cmake -WITH_WSREP .

Note: -DWITH_WSREP=ON does not work, it has to be -WITH_WSREP specifically, which differs from 10.1. It could be that this change was made in 10.2 or in later versions. It may be good to check this to see if 10.2, 10.3 and 10.5 have a different option requirement.

Also, on a related note, I would assume that -DWITH_INNODB_DISALLOW_WRITES=ON is indeed no longer needed past 10.1 as the manual states, but am not sure, hence assigning this to Jan for his evaluation first. jplindst Please assign to jacob.moorman once you confirm whether -DWITH_INNODB_DISALLOW_WRITES=ON is indeed no longer needed after 10.1. Thank you both.