Warn on unused auto variables.

To do so we have to wait until we know that the type of a variable has been
deduced. Sema::FinalizeDeclaration is the first callback that is used for
decl with or without initializers.

llvm-svn: 171458
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 624f405..61791b2 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -4537,8 +4537,6 @@
   // member, set the visibility of this variable.
   if (NewVD->getLinkage() == ExternalLinkage && !DC->isRecord())
     AddPushedVisibilityAttribute(NewVD);
-  
-  MarkUnusedFileScopedDecl(NewVD);
 
   return NewVD;
 }
@@ -7348,6 +7346,9 @@
   if (!VD)
     return;
 
+  if (VD->isFileVarDecl())
+    MarkUnusedFileScopedDecl(VD);
+
   // Now we have parsed the initializer and can update the table of magic
   // tag values.
   if (!VD->hasAttr<TypeTagForDatatypeAttr>() ||