From compiling go there were 260 functions where XOR was needed.

Much of the required changes for implementing XOR were already
done in 12813.

Change-Id: I5a68aa028f5ed597bc1d62cedbef3620753dfe82
Reviewed-on: https://go-review.googlesource.com/12901Reviewed-by: Keith Randall <khr@golang.org>