collate/tools/colcmp: fix build breakage for darwin.

This used to work.
This still doesn't work fully, but it will have to do for now.

Change-Id: Idabfdf9b5ebffad098962b9d5c817e1febc09837
Reviewed-on: https://go-review.googlesource.com/9800
Reviewed-by: Nigel Tao <nigeltao@golang.org>
1 file changed