make new warning not ignored by default

Author: spall

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -10639,7 +10639,7 @@ def err_vector_index_out_of_range : Error<
   "vector element index %0 is out of bounds">;
 def warn_vector_index_out_of_range : Warning<
   err_vector_index_out_of_range.Summary>,
-  InGroup<VectorOutOfRange>, DefaultIgnore;
+  InGroup<VectorOutOfRange>;
 
 def err_vec_builtin_non_vector : Error<
  "%select{first two|all}1 arguments to %0 must be vectors">;