Use an unused-except-in-Debug variable.

llvm-svn: 126240
diff --git a/clang/lib/AST/ASTContext.cpp b/clang/lib/AST/ASTContext.cpp
index df92d11..6d0b6d7 100644
--- a/clang/lib/AST/ASTContext.cpp
+++ b/clang/lib/AST/ASTContext.cpp
@@ -874,7 +874,7 @@
   case Type::Auto: {
     const AutoType *A = cast<AutoType>(T);
     assert(A->isDeduced() && "Cannot request the size of a dependent type");
-    return getTypeInfo(cast<AutoType>(T)->getDeducedType().getTypePtr());
+    return getTypeInfo(A->getDeducedType().getTypePtr());
   }
 
   case Type::Paren: