Allow disabling libXML in Clang's CMake build

Allow disabling libXML in Clang's CMake build

We used this before the Precise upgrade for the same purpose I'm
reintroducing it; the sysroot we are building in lacks libXML but
Clang's CMake build finds it on the host system.

R=stichnot@google.com, bradnelson@chromium.org
BUG= https://bugs.chromium.org/p/nativeclient/issues/detail?id=4394

Committed: e34aaa1fd835c13131bf82b16b768253e14e9247

[Derek Schuff, 2017-03-23 22:38:30]

dschuff@chromium.org changed reviewers:
+ stichnot@chromium.org

[stichnot1, 2017-03-23 23:03:07]

stichnot@google.com changed reviewers:
+ stichnot@google.com

[stichnot1, 2017-03-23 23:03:08]

lgtm

[Derek Schuff, 2017-03-23 23:06:25]

Description was changed from

==========
Allow disabling libXML in Clang's CMake build

We used this before the Precise upgrade for the same purpose I'm
reintroducing it; the sysroot we are building in lacks libXML but
Clang's CMake build finds it on the host system.

R=bradnelson@chromium.org
BUG= https://bugs.chromium.org/p/nativeclient/issues/detail?id=4394
==========

to

==========
Allow disabling libXML in Clang's CMake build

We used this before the Precise upgrade for the same purpose I'm
reintroducing it; the sysroot we are building in lacks libXML but
Clang's CMake build finds it on the host system.

R=stichnot@google.com, bradnelson@chromium.org
BUG= https://bugs.chromium.org/p/nativeclient/issues/detail?id=4394

Committed: e34aaa1fd835c13131bf82b16b768253e14e9247
==========

[Derek Schuff, 2017-03-23 23:06:26]

Committed patchset #1 (id:1) manually as
e34aaa1fd835c13131bf82b16b768253e14e9247 (presubmit successful).