reproducible results: use stat instead of du

[marcpawl]

du is an estimate of the size of the files. (man du).
This estimate can vary greatly from run to run, and thus provide different results when trying to get a reproducible build.
USIZE=du $DU_ARGS "$archdir" | awk '{print $1}'
should be changed to use stat instead.

[megastep]

The main problem is that stat seems to be a BSD command and is probably not available on many System V UNIX systems.

That said, it might be a good idea to try to use it first and then fall back to the du use if it is not available.