Add a hasExternalStorageAsWritten helper. No functionality change.

It is possible that some of the current uses of
"getStorageClassAsWritten() == SC_Extern" should use this but I don't know
enough about SC_PrivateExtern to change and test them.

llvm-svn: 176606
diff --git a/clang/lib/AST/Decl.cpp b/clang/lib/AST/Decl.cpp
index b8439ca..257e59c 100644
--- a/clang/lib/AST/Decl.cpp
+++ b/clang/lib/AST/Decl.cpp
@@ -1049,8 +1049,7 @@
   }
 
   if (const VarDecl *Var = dyn_cast<VarDecl>(D)) {
-    if (Var->getStorageClassAsWritten() == SC_Extern ||
-        Var->getStorageClassAsWritten() == SC_PrivateExtern) {
+    if (Var->hasExternalStorageAsWritten()) {
       if (Var->isInAnonymousNamespace() &&
           !Var->getDeclContext()->isExternCContext())
         return LinkageInfo::uniqueExternal();
@@ -1600,9 +1599,8 @@
   // AST for 'extern "C" int foo;' is annotated with 'extern'.
   if (hasExternalStorage())
     return DeclarationOnly;
-  
-  if (getStorageClassAsWritten() == SC_Extern ||
-       getStorageClassAsWritten() == SC_PrivateExtern) {
+
+  if (hasExternalStorageAsWritten()) {
     for (const VarDecl *PrevVar = getPreviousDecl();
          PrevVar; PrevVar = PrevVar->getPreviousDecl()) {
       if (PrevVar->getLinkage() == InternalLinkage)