[PATCH] Use a single data structure to store all user variables in DwarfDebug

[Alexey Samsonov]

================
Comment at: lib/CodeGen/AsmPrinter/DwarfDebug.cpp:1207
@@ -1205,3 +1206,3 @@
 
     DIVariable DV(Var);
     LexicalScope *Scope = nullptr;
----------------
David Blaikie wrote:
> You can probably push DIVariable DV(Var) up to DIVariable DV(I.first) and Processed.count(DV) (I think the implicit conversion to MDNode* will work out here). Just to avoid having that raw MDNode* lying around.
> 
> Not necessary, up to you if you want to do it at all and either in this commit or separately.
Done.

http://reviews.llvm.org/D3579