mksysinfo: use rlimit64 if available when we use getrlimit64

This makes no difference on most systems, because <sys/resource.h>
renames the type appropriately anyhow, but apparently it makes a
difference on AIX.

Change-Id: Iddc29371c649f4795029c42d6c960c7e84e2d7a1
Reviewed-on: https://go-review.googlesource.com/88076
Reviewed-by: Than McIntosh <thanm@google.com>
3 files changed