In the non-x64 fallback code path, use the system ld.

The 32-bit buildbots are set up with gold as the system ld, and
fail when this code causes them to fall back to bfd ld.
Review URL: https://chromiumcodereview.appspot.com/9328007

git-svn-id: http://src.chromium.org/svn/trunk/deps/third_party/gold@120423 4ff67af0-8c30-449e-8e8b-ad334ec8d88c