[ORC] Re-apply 286620 with fixes for the ErrorSuccess class.

llvm-svn: 286639
diff --git a/llvm/lib/ExecutionEngine/Orc/OrcError.cpp b/llvm/lib/ExecutionEngine/Orc/OrcError.cpp
index 64472f9..48dcd44 100644
--- a/llvm/lib/ExecutionEngine/Orc/OrcError.cpp
+++ b/llvm/lib/ExecutionEngine/Orc/OrcError.cpp
@@ -43,6 +43,8 @@
       return "Unexpected RPC call";
     case OrcErrorCode::UnexpectedRPCResponse:
       return "Unexpected RPC response";
+    case OrcErrorCode::UnknownRPCFunction:
+      return "Unknown RPC function";
     }
     llvm_unreachable("Unhandled error code");
   }