Revert. This isn't the correct way to go.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@108478 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.h b/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.h
index 8621637..46733d6 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.h
+++ b/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.h
@@ -385,7 +385,7 @@
   void visitBr(const BranchInst &I);
   void visitSwitch(const SwitchInst &I);
   void visitIndirectBr(const IndirectBrInst &I);
-  void visitUnreachable(const UnreachableInst &I);
+  void visitUnreachable(const UnreachableInst &I) { /* noop */ }
 
   // Helpers for visitSwitch
   bool handleSmallSwitchRange(CaseRec& CR,