Add missing copyright header.

Author: lhames

orc-rt/lib/executor/orc-rt-executor.cpp

@@ -1,3 +1,15 @@
+//===- orc-rt-executor.cpp - Placeholder implementation for orc-rt --------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// Placeholder implementation file for initial orc-rt checkin.
+//
+//===----------------------------------------------------------------------===//
+
 #include <stdio.h>
 
 extern "C" void orc_rt(void) { printf("hello, world!\n"); }