Implement __is_empty.  Patch by Sean Hunt.

llvm-svn: 79143
diff --git a/clang/lib/Parse/ParseExpr.cpp b/clang/lib/Parse/ParseExpr.cpp
index 6e7deef..57604a8 100644
--- a/clang/lib/Parse/ParseExpr.cpp
+++ b/clang/lib/Parse/ParseExpr.cpp
@@ -815,6 +815,7 @@
   case tok::kw___is_class:
   case tok::kw___is_enum:
   case tok::kw___is_union:
+  case tok::kw___is_empty:
   case tok::kw___is_polymorphic:
   case tok::kw___is_abstract:
   case tok::kw___has_trivial_constructor: