Define old stat functions only if needed

Define old stat functions only if needed

When HAVE_LONG_LONG_OFF_T is defined, those old stat functions aren't
used and strace won't link since they use realprintstat which isn't
defined when HAVE_LONG_LONG_OFF_T is defined.

* file.c (convertoldstat, sys_oldstat, sys_oldfstat, sys_oldlstat):
Define only if HAVE_LONG_LONG_OFF_T isn't defined.