Add an additional check to UnwindAssembly_x86::AugmentUnwindPlanFromCallSite

Add an additional check to UnwindAssembly_x86::AugmentUnwindPlanFromCallSite
which will verify if the eh_frame instructions include details about
the prologue or not.  Both clang and gcc include prologue instructions
but there's no requirement for them to do so -- and I'm sure we'll
have to interoperate with a compiler that doesn't generate prologue
info at some point.

I don't have any compilers that omit the prologue instructions so the
testing was of the "makre sure augmented unwind info is still created".
With an eh_frame without prologue, this code should reject the
augmentation scheme altogether and we should fall back to using assembly
instruction profiling.

llvm-svn: 225771