Add the Microsoft __is_interface_class type trait.
Patch by Andy Gibbs!

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@164591 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/docs/LanguageExtensions.html b/docs/LanguageExtensions.html
index 21ac627..8c0e5b7 100644
--- a/docs/LanguageExtensions.html
+++ b/docs/LanguageExtensions.html
@@ -1007,6 +1007,7 @@
   <li><code>__is_convertible_to</code> (Microsoft)</li>
   <li><code>__is_empty</code> (GNU, Microsoft)</li>
   <li><code>__is_enum</code> (GNU, Microsoft)</li>
+  <li><code>__is_interface_class</code> (Microsoft)</li>
   <li><code>__is_pod</code> (GNU, Microsoft)</li>
   <li><code>__is_polymorphic</code> (GNU, Microsoft)</li>
   <li><code>__is_union</code> (GNU, Microsoft)</li>