Declaration of multi-module libraries with differing targets

[JesusMcCloud]

How to correctly list a library consisting of multiple modules, where some modules support more targets than others?

As a concrete example, Signum, which I am maintaining now support every target but Wasm/WASI, except for the Supreme module, which only supports iOS, JVM, and Android. The other modules are still very much useful on other platforms, even without the Supreme module.