Sprinkle llvm_unreachable around to placate GCC's -Wreturn-type.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@159860 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/AST/CommentParser.cpp b/lib/AST/CommentParser.cpp
index 14a2d85..2df3759 100644
--- a/lib/AST/CommentParser.cpp
+++ b/lib/AST/CommentParser.cpp
@@ -390,6 +390,7 @@
   case tok::html_greater:
     llvm_unreachable("should not see this token");
   }
+  llvm_unreachable("bogus token kind");
 }
 
 FullComment *Parser::parseFullComment() {
@@ -410,5 +411,3 @@
 
 } // end namespace comments
 } // end namespace clang
-
-