Revert "Decouple dllexport/dllimport from linkage"

Revert this for now until I fix an issue in Clang with it.

This reverts commit r199204.

llvm-svn: 199207
diff --git a/llvm/lib/Target/X86/X86Subtarget.cpp b/llvm/lib/Target/X86/X86Subtarget.cpp
index 6f724b4..b183ed0 100644
--- a/llvm/lib/Target/X86/X86Subtarget.cpp
+++ b/llvm/lib/Target/X86/X86Subtarget.cpp
@@ -55,7 +55,7 @@
 ClassifyGlobalReference(const GlobalValue *GV, const TargetMachine &TM) const {
   // DLLImport only exists on windows, it is implemented as a load from a
   // DLLIMPORT stub.
-  if (GV->hasDLLImportStorageClass())
+  if (GV->hasDLLImportLinkage())
     return X86II::MO_DLLIMPORT;
 
   // Determine whether this is a reference to a definition or a declaration.