how to configure for libitm?

[Jack Howarth]

   I am trying to test the proposed merge of the transactional memory branch on
x86_64-apple-darwin11. Since the posted patches on gcc-patches seem to have 
malformed sections, I used the merge patches from http://quesejoda.com/redhat/tm-branch-diffs-from-trunk-at-180744/
instead (with the adjustment of moving the patch for crtstuff.c from gcc to libgcc).
However I don't see able to get libitm to build. The configure changes don't seem to have
any explicit transactional memory options and --enable-libitm seems to be ignored.
>From the changes in configure.ac, darwin should be a supported target. Thanks in
advance for any clues.
          Jack