Replace an isa/cast with a dyn_cast.

llvm-svn: 124542
diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index 49c0b35..66ac9fa 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -457,8 +457,8 @@
 
 void CodeGenModule::SetCommonAttributes(const Decl *D,
                                         llvm::GlobalValue *GV) {
-  if (isa<NamedDecl>(D))
-    setGlobalVisibility(GV, cast<NamedDecl>(D));
+  if (const NamedDecl *ND = dyn_cast<NamedDecl>(D))
+    setGlobalVisibility(GV, ND);
   else
     GV->setVisibility(llvm::GlobalValue::DefaultVisibility);