dh_dwz with --multifile inside a binary package

How to do this:

• efficiently (xargs)
• without clashes (the cmd-line limits the number of files in the multifile; we may need multiple multifiles)
• reproducibly (multiple multifile with distinct names; must be deterministic what they are called and what goes in them)
• maintainable
• the multifile has to go into the -dbg/-dbgsym

Open question, should we set a(n optional) max limit for number of ELF binaries that goes into a multifile?