Use libunwindstack instead of libbacktrace.

Replace all instances of libbacktrace code with equivalent
libunwindstack code.

Test: Run 037-cfi test in optimized, interpreter, jit modes.
Test: Ran 004-ThreadStress in a loop for optimized, interpreter, jit modes.
Test: Forced an ANR and verified native stacks are correct, and that
Test: native stacks correctly stop before java stacks.
Change-Id: I642ffd61b731dae6a68a5ba9453485a79f608d28
23 files changed