Add support for riscv 64 vlenb.

The vlenb register is used for some unwinding information, so add
gathering it. Also, rename some of the machine constants to use
better names.

Added an offline test that uses the vlenb register to do the unwind.
Added a remote unwind test for the bionic local terminate.

Bug: 318768887

Test: Ran unit tests.
Test: Ran 137-cfi and verified a full stack generated.
Change-Id: Ia72394033b4be46a3f29d519879b88ed933ab5ce
22 files changed
tree: 5d69b91fec07b97c1521a34eccb557e246faac07
  1. libunwindstack/
  2. OWNERS
  3. PREUPLOAD.cfg