Add a first unit test for the arm64 instruction profiled unwind

plan generator.

Fix a small bug in EmulateInstructionARM64::GetFramePointerRegister
which was returning the stack pointer reg instead of fp, prevented
the unwinder from recognizing the switch to using the fp in a
function. (<rdar://problem/28663117>)

Add a new eContextRestoreStackPointer context hint so that the arm64
emulator can flag when the frame pointer value is copied back in to
the stack pointer and that should be used to compute the canonical
frame address again in an epilogue sequence.  (<rdar://problem/28704862>)

Small changes to UnwindAssemblyInstEmulation to have a method we can
call without a live process/thread/etc for unit tests.

<rdar://problem/28663117> 
<rdar://problem/28704862> 
<rdar://problem/28509178> 

llvm-svn: 283847