Revert r260388 "[MS ABI] Never reference dllimport'd vtables"

This caused the compiler to fail with "invalid linkage type
for global declaration" (PR26569).

llvm-svn: 260449
diff --git a/clang/lib/AST/VTableBuilder.cpp b/clang/lib/AST/VTableBuilder.cpp
index b728b27..bae0186 100644
--- a/clang/lib/AST/VTableBuilder.cpp
+++ b/clang/lib/AST/VTableBuilder.cpp
@@ -2548,6 +2548,7 @@
     // Only include the RTTI component if we know that we will provide a
     // definition of the vftable.
     HasRTTIComponent = Context.getLangOpts().RTTIData &&
+                       !MostDerivedClass->hasAttr<DLLImportAttr>() &&
                        MostDerivedClass->getTemplateSpecializationKind() !=
                            TSK_ExplicitInstantiationDeclaration;