Add a hasExternalLinkage helper. No functionality change.

llvm-svn: 176607
diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
index 46010e4..22a31e0 100644
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -11364,7 +11364,7 @@
     Consumer.HandleVTable(Class, VTablesUsed[Canonical]);
 
     // Optionally warn if we're emitting a weak vtable.
-    if (Class->getLinkage() == ExternalLinkage &&
+    if (Class->hasExternalLinkage() &&
         Class->getTemplateSpecializationKind() != TSK_ImplicitInstantiation) {
       const FunctionDecl *KeyFunctionDef = 0;
       if (!KeyFunction ||