Rudimentary support for Doxygen \retval command

...so that at least a preceding \param etc. that lacks a description gets a
-Wdocumentation warning (instead of erroneously treating the \retval ... text as
its paragraph).

Differential Revision: https://reviews.llvm.org/D66350

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@369345 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/include/clang/AST/CommentCommands.td b/include/clang/AST/CommentCommands.td
index 958ee03..3b0d160 100644
--- a/include/clang/AST/CommentCommands.td
+++ b/include/clang/AST/CommentCommands.td
@@ -139,6 +139,7 @@
 def Pre        : BlockCommand<"pre">;
 def Remark     : BlockCommand<"remark">;
 def Remarks    : BlockCommand<"remarks">;
+def Retval     : BlockCommand<"retval">;
 def Sa         : BlockCommand<"sa">;
 def See        : BlockCommand<"see">;
 def Since      : BlockCommand<"since">;