xmlto: upgraded package to upstream

Upgraded app-text/xmlto to version 0.0.28-r6 for all.
This fixes CC misuse.

BUG=None
TEST=CQ passes

Change-Id: I7e0f0264e4a3ee866138f1f3e4063bdfc8cf09c1
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/overlays/portage-stable/+/2971624
Tested-by: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Chris McDonald <cjmcdonald@chromium.org>
Commit-Queue: Mike Frysinger <vapier@chromium.org>
6 files changed