Current multiplatform support seems very Gradle-centric. Are non-Gradle projects supported? Someday? Ant perhaps?
I believe that while Ant and Maven were specifically designed to be used for Java projects, Gradle was designed to be adaptable for building any language, so probably not.
If you can’t live without ant, you can use it from inside gradle.
Though I do not really know, why you would do that. I was a great fan of maven in my own time, but now gradle beats it in any possible sense.
There’s some limited support of multiplatform projects in maven, though it’s not being developed actively ATM.
For example kotlinx.html is a maven multiplatform library.