arch-sparc: Rewrite unused array in tgt_stat64 for mac

On Mac (tested on Mac Mini M2 Pro) the src/arch/sparc/linux/linux.hh was
uncompilable due to `int64_t __unused[3]` not working with the Mac
GLIB's `__unused` definition. This was therefore rewritten.

Change-Id: I8094a54ccf8dedb8e63ef05770e48eef7012262c
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/68838
Maintainer: Bobby Bruce <bbruce@ucdavis.edu>
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Melissa Jost <mkjost@ucdavis.edu>
1 file changed