Add support for getting TLS on all arches.

The guest support was refactored and in that change, all arm32 support
was removed. Add the ability for a thread to run as an arm32 guest.

In addition, add code to handle getting the TLS data on all different
arches.

Test: Unit tests pass.
Test: Ran on a device that supports an arm32 guest and verified that
Test: the tombstone has the guest set properly.
Change-Id: I6ab61f91e59bdc0981d590aeb6c509632b1cc03a