Comment parsing: add CommentOptions to allow specifying custom comment block commands

Add an ability to specify custom documentation block comment commands via a new
class CommentOptions.  The intention is that this class will hold future
customizations for comment parsing, including defining documentation comments
with specific numbers of parameters, etc.

CommentOptions instance is a member of LangOptions.

CommentOptions is controlled by a new command-line parameter
-fcomment-block-commands=Foo,Bar,Baz.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@175892 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Frontend/ASTUnit.cpp b/lib/Frontend/ASTUnit.cpp
index fcc8ea8..1e7d404 100644
--- a/lib/Frontend/ASTUnit.cpp
+++ b/lib/Frontend/ASTUnit.cpp
@@ -573,6 +573,11 @@
 
     // Initialize the ASTContext
     Context.InitBuiltinTypes(*Target);
+
+    // We didn't have access to the comment options when the ASTContext was
+    // constructed, so register them now.
+    Context.getCommentCommandTraits().registerCommentOptions(
+        LangOpt.CommentOpts);
   }
 };