Support unwinding though the switch interpreter.

Wrap the switch interpreter in small assembly method which defines
DEX PC in CFI and thus it allows libunwind to backtrace through it.

Bug: 22414682
Test: testrunner.py --host -t 137
Test: testrunner.py --target -t 137
Change-Id: I31dad9f0fb446151baaa99234b64f25c8ca2fa87
22 files changed