Update libxo to 0.6.3

This fixes the 02 testcases on i386 (at least), and may fix the testcases
in general on 32-bit platforms

Differential Revision: https://reviews.freebsd.org/D7052
Approved by: phil (maintainer)
Approved by: re (gjb)
Reported by: asomers
Reviewed by: phil
Submitted by: phil
Sponsored by: EMC / Isilon Storage Division