We need to ensure %gs:20 is set up early enough for -fstack-protector-strong
on x86, and that __set_tls doesn't get stack protector checks because it's a
prerequisite for them. x86 devices/emulators won't boot without this.
Bug: http://b/26073874
Change-Id: Icf0d34294648cc0c8cb406a3617befe0d45c525a
6c54ddd20f