Fix S360 issue by using "use strict" for javascript code. (microsoft#…

…9128)

docs/c_cxx/doxygen-header.html

@@ -16,7 +16,7 @@
 <!--END DISABLE_INDEX-->
 <script type="text/javascript" src="$relpath^jquery.js"></script>
 <script type="text/javascript" src="$relpath^dynsections.js"></script>
-<script async src="https://www.googletagmanager.com/gtag/js?id=UA-156955408-1"></script><script> window.dataLayer = window.dataLayer || []; function gtag(){dataLayer.push(arguments);} gtag('js', new Date()); gtag('config', 'UA-156955408-1'); </script> <script type="text/javascript" src="/assets/js/vendor/lunr.min.js"></script> <script type="text/javascript" src="/assets/js/just-the-docs.js"></script> 
+<script async src="https://www.googletagmanager.com/gtag/js?id=UA-156955408-1"></script><script type="text/javascript">"use strict"; window.dataLayer = window.dataLayer || []; function gtag(){dataLayer.push(arguments);} gtag('js', new Date()); gtag('config', 'UA-156955408-1'); </script> <script type="text/javascript" src="/assets/js/vendor/lunr.min.js"></script> <script type="text/javascript" src="/assets/js/just-the-docs.js"></script>
 $treeview
 $search
 $mathjax