Handle the case where we are stepping through code with no symbols, so we can't really find the function start PC 
and so the StackID changes with every step.  Do so by checking the parent frame ID, and if it hasn't changed,
then we haven't stepped in.

rdar://problem/14516227


git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@187094 91177308-0d34-0410-b5e6-96231b3b80d8