The build is customizable by using CMake options in the configure step

$ cmake -D <option-name>=<value> .

-D

Create or update a cmake cache entry.

When cmake is first run in an empty build tree, it creates a CMakeCache.txt file

  and populates it with customizable settings for the project.

  (a setting that takes priority over the project’s default value)

i.e.

cmake -D BUILD_RDIFF=OFF .