Add recognition for another x86 epilogue sequence (ret followed by
a nop).  Fixes an instruction stepping problem when trying to step
over the final instructions of an epilogue.
<rdar://problem/18068877> 


git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@221241 91177308-0d34-0410-b5e6-96231b3b80d8