MS ABI: Don't try to emit VF/VB-Tables for extern class templates

There will be an explicit template instantiation in another translation
unit which will provide the definition of the VF/VB-Tables.

This fixes PR22932.

llvm-svn: 232680

clang/lib/CodeGen/CodeGenModule.cpp

@@ -1851,7 +1851,8 @@ CodeGenModule::CreateOrReplaceCXXRuntimeVariable(StringRef Name,
     OldGV->eraseFromParent();
   }
 
-  if (supportsCOMDAT() && GV->isWeakForLinker())
+  if (supportsCOMDAT() && GV->isWeakForLinker() &&
+      !GV->hasAvailableExternallyLinkage())
     GV->setComdat(TheModule.getOrInsertComdat(GV->getName()));
 
   return GV;