Add eXtensible Systems, Inc. copyright to LLVM

Change-Id: Ibed3bb022494871c42f4aa2a940149db9158f883

NOTICES.txt

diff --git a/NOTICES.txt b/NOTICES.txt
index ffa210a..58d6d97 100644
--- a/NOTICES.txt
+++ b/NOTICES.txt
@@ -5864,6 +5864,13 @@
 NOTICE llvm
 URL: https://llvm.org/
 
+LLVM System Interface Library
+-------------------------------------------------------------------------------
+The LLVM System Interface Library is licensed under the Illinois Open Source
+License and has the following additional copyright:
+
+Copyright (C) 2004 eXtensible Systems, Inc.
+
 University of Illinois/NCSA
 Open Source License