[NaCl SDK] Always remove libraries before creating them.

Without this ar will always add to the existing
library which leads to issues when sources/objects are
removed/renamed.

BUG=218090
R=noelallen@chromium.org

Review URL: https://codereview.chromium.org/24605003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@225729 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 225729
sync: beginnings of a sync/api implementation of sessions datatype

Based off of https://codereview.chromium.org/23018004/

BUG=80194, 98892
R=shashishekhar@chromium.org, zea@chromium.org

Review URL: https://codereview.chromium.org/18600013

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@225731 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 225731