Add DiagGroup to NoRandomizeLayout attribute

All attributes that emit warnings are required
to be members of a warning group; this is checked
by the clang-test regression suite.

Author: connorkuehl

clang/include/clang/Basic/DiagnosticASTKinds.td

@@ -347,6 +347,6 @@ def warn_unnecessary_packed : Warning<
 // RandStruct implementation
 def warn_randomize_attr_conflict : Warning<
   "struct declared with 'randomize_layout' and 'no_randomize_layout' attributes;"
-  "attribute 'no_randomize_layout' takes precedence">;
+  "attribute 'no_randomize_layout' takes precedence">, InGroup<DiagGroup<"no-randomize-layout">>;
 
 }