Fix LexicalScope reset in LiveDebugVariables.cpp

[kariddi]

Summary

Hello,

I noticed by inspection that in LiveDebugVariables.cpp we don't actually reset the LexicalScope when we clear() the LDVImpl object.
This might create problems if we rely on clearing the object.
This patch fixes that.

[dblaikie]

It's harmless enough - I think the only particular benefit is in 'releaseMemory', causing this to release the memory of the LexicalScopes too.

[kariddi]

Thanks, committed in r220545

lib/CodeGen/LiveDebugVariables.cpp

            "Dbg values are not emitted in LDV");
     EmitDone = false;
     ModifiedMF = false;
+    LS.reset();
   }
 
   /// mapVirtReg - Map virtual register to an equivalence class.