Handle an edge case where we step into a function whose UnwindPlan
defines a Return Address register (e.g. lr on arm) but the RA register
hasn't been saved anywhere yet -- it is still in a live reg.
<rdar://problem/13503130> 


git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@179431 91177308-0d34-0410-b5e6-96231b3b80d8