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These are produced by the "cat" command to makeqstrdefs.py, to allow it to
not update unchanged files.  cmake doesn't know about them and so they are
not removed on a "clean".

This triggered a bug in makeqstrdefs.py where it would not recreate a
deleted output file (which is removed by clean) if a stale hash file with a
valid hash still existed.

Listing them as byproducts will cause them to be deleted on clean.
Signed-off-by: Trent Piepho <tpiepho@gmail.com>