Get the dll storage class right for structors of classes exported/imported via explicit instantiation (PR23667)

This is a follow-up to r238266. It turned out structors are codegened through a different path,
and didn't get the storage class set in EmitGlobalFunctionDefinition.

llvm-svn: 238443
diff --git a/clang/lib/CodeGen/CodeGenModule.h b/clang/lib/CodeGen/CodeGenModule.h
index feef6c2..3500096 100644
--- a/clang/lib/CodeGen/CodeGenModule.h
+++ b/clang/lib/CodeGen/CodeGenModule.h
@@ -1018,6 +1018,9 @@
     F->setLinkage(getFunctionLinkage(GD));
   }
 
+  /// Set the DLL storage class on F.
+  void setFunctionDLLStorageClass(GlobalDecl GD, llvm::Function *F);
+
   /// Return the appropriate linkage for the vtable, VTT, and type information
   /// of the given class.
   llvm::GlobalVariable::LinkageTypes getVTableLinkage(const CXXRecordDecl *RD);