The filesystem iterator takes `stat` data from disk and puts them into
index entries, which use 32 bit ints for time (the seconds portion) and
filesize.  However, on most systems these are not 32 bit, thus will
typically invoke a warning.

Most users ignore these fields entirely.  Diff and checkout code do use
the values, however only for the cache to determine if they should check
file modification.  Thus, this is not a critical error (and will cause a
hash recomputation at worst).