Add __newlib_thread_exit() to the ARM newlib.
Add __newlib_thread_exit() to the ARM newlib.

currently the thread exit hook will only invoke cleanup of the current thread.
This includes flushing the stdio buffers.
Review URL: http://codereview.chromium.org/1631028

git-svn-id: 721b910a23eff8a86f00c8fd261a7587cddf18f8@2083 fcba33aa-ac0c-11dd-b9e7-8d5594d729c2

nacl-webkit/native_client,nacl-webkit/native_client,sbc100/native_client,sbc100/native_client,nacl-webkit/native_client,nacl-webkit/native_client,sbc100/native_client,nacl-webkit/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client