For cross-compilation I need to specify the MCU type as a option to the Ada, C and theoretically C++ compiler.

How can I do that and in a way that it is also applied when building the dependencies?

At https://alire.ada.dev/docs/catalog-format-spec.html#build-profiles-and-switches I saw how I can replace e.g. the optimization options per build profile.

However, this is not adding, but replacing and, beyond that, seems to only apply to the Ada compiler.