RawCommentList::addComment: fix the assertion so it actually checks that new comment is after the last one (change Comments[0] to Comments.back()), and handle the case of two consecutive comments, e.g. /** *//* */.  There is already a testcase for that (but it didn't trigger the assert because the assert itself was wrong).

llvm-svn: 158882
diff --git a/clang/lib/AST/RawCommentList.cpp b/clang/lib/AST/RawCommentList.cpp
index 0651029..1baa9b8 100644
--- a/clang/lib/AST/RawCommentList.cpp
+++ b/clang/lib/AST/RawCommentList.cpp
@@ -159,8 +159,10 @@
     return;
 
   assert((Comments.empty() ||
+          Comments.back().getSourceRange().getEnd() ==
+              RC.getSourceRange().getBegin() ||
           SourceMgr.isBeforeInTranslationUnit(
-              Comments[0].getSourceRange().getEnd(),
+              Comments.back().getSourceRange().getEnd(),
               RC.getSourceRange().getBegin())) &&
          "comments are not coming in source order");