CMake replaces `configure` scripts. It would be difficult to imagine what multi-architecture support in a single build directory / command-line invocation would look like.

Instead, what we do is to wrap calls to CMake in a script that makes choices about build directories, which flavours to build by default, which mobile SDKs exist, etc. When producing a release, we notably don't use this, because we are precisely interested in building for each architecture in parallel on different machines.