arm: Add thumb target and associated fixes

Add arm_thumb=1 to GYP_DEFINES to enable

BUG=29203

Review URL: http://codereview.chromium.org/463027

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@33799 0039d316-1c4b-4281-b951-d872f2087c98
2 files changed