Add more missing license headers

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@258198 91177308-0d34-0410-b5e6-96231b3b80d8

utils/gen_link_script/gen_link_script.py

@@ -1,4 +1,13 @@
 #!/usr/bin/env python
+#===----------------------------------------------------------------------===##
+#
+#                     The LLVM Compiler Infrastructure
+#
+# This file is dual licensed under the MIT and the University of Illinois Open
+# Source Licenses. See LICENSE.TXT for details.
+#
+#===----------------------------------------------------------------------===##
+
 import os
 import sys