Fix unused variable warning. NFCI.

llvm-svn: 356839
diff --git a/clang/lib/CodeGen/CGCXX.cpp b/clang/lib/CodeGen/CGCXX.cpp
index af20856..adaeacf 100644
--- a/clang/lib/CodeGen/CGCXX.cpp
+++ b/clang/lib/CodeGen/CGCXX.cpp
@@ -222,7 +222,7 @@
     bool DontDefer, ForDefinition_t IsForDefinition) {
   auto *MD = cast<CXXMethodDecl>(GD.getDecl());
 
-  if (auto *DD = dyn_cast<CXXDestructorDecl>(MD)) {
+  if (isa<CXXDestructorDecl>(MD)) {
     // Always alias equivalent complete destructors to base destructors in the
     // MS ABI.
     if (getTarget().getCXXABI().isMicrosoft() &&