That wouldn't make sense. The java compiler takes source files and produces class files on a 1-to-1 basis. What would you expect a multi-targeted compile to do? Replicate all of the outputs in all of the directories? Or randomly scatter classes among them?
If you just want to make multiple copies of a set of classes, just run a copy after the compile. That's the Unix approach - don't make 1 complex specialized program when you can make 2 simple general ones do the job.
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subject: Multiple dist directories in "javac" tasks in Ant