xfsprogs: avoid use of si_tid in struct xlog_split_item

xfsprogs: avoid use of si_tid in struct xlog_split_item

In Android's bionic libc (as well as the Linux kernel's
include/uapi/asm-generic/siginfo.h), si_tid is a #define to provide
backwards compatibility for the timerid in the siginfo structure.
This breaks the compile of logprint/log_misc.c.  Change this to be
si_xtid in order to avoid a namespace collision

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Dave Chinner <david@fromorbit.com>