Fix compile warnings found using nvcc 11.4 (#9101)

While looking into a `compute-sanitizer` issue, I found the problem with the tool had been fixed in 11.4. Building libcudf in 11.4 uncovered some new compile warnings which are fixed in this PR. All the warnings were identifying unused variables.

Authors:
  - David Wendt (https://github.com/davidwendt)

Approvers:
  - Nghia Truong (https://github.com/ttnghia)
  - Vyas Ramasubramani (https://github.com/vyasr)
  - Mark Harris (https://github.com/harrism)

URL: #9101

cpp/src/binaryop/compiled/binary_ops.cu

@@ -43,7 +43,7 @@ struct scalar_as_column_device_view {
   template <typename T, std::enable_if_t<(is_fixed_width<T>())>* = nullptr>
   return_type operator()(scalar const& s,
                          rmm::cuda_stream_view stream,
-                         rmm::mr::device_memory_resource* mr)
+                         rmm::mr::device_memory_resource*)
   {
     auto& h_scalar_type_view = static_cast<cudf::scalar_type_t<T>&>(const_cast<scalar&>(s));
     auto col_v =
@@ -201,7 +201,6 @@ struct null_considering_binop {
                                      rmm::cuda_stream_view stream,
                                      rmm::mr::device_memory_resource* mr) const
   {
-    std::unique_ptr<column> out;
     // Create device views for inputs
     auto const lhs_dev_view = get_device_view(lhs);
     auto const rhs_dev_view = get_device_view(rhs);

cpp/src/io/orc/reader_impl.cu

@@ -176,7 +176,6 @@ size_t gather_stream_info(const size_t stripe_index,
                           const orc::StripeInformation* stripeinfo,
                           const orc::StripeFooter* stripefooter,
                           const std::vector<int>& orc2gdf,
-                          const std::vector<orc_column_meta>& gdf2orc,
                           const std::vector<orc::SchemaType> types,
                           bool use_index,
                           size_t* num_dictionary_entries,
@@ -1203,7 +1202,6 @@ table_with_metadata reader::impl::read(size_type skip_rows,
                                                           stripe_info,
                                                           stripe_footer,
                                                           _col_meta.orc_col_map[level],
-                                                          selected_columns,
                                                           _metadata->get_types(),
                                                           use_index,
                                                           &num_dict_entries,

cpp/src/merge/merge.cu

@@ -225,11 +225,10 @@ struct column_merger {
   explicit column_merger(index_vector const& row_order) : row_order_(row_order) {}
 
   template <typename Element, CUDF_ENABLE_IF(not is_rep_layout_compatible<Element>())>
-  std::unique_ptr<column> operator()(
-    column_view const& lcol,
-    column_view const& rcol,
-    rmm::cuda_stream_view stream,
-    rmm::mr::device_memory_resource* mr = rmm::mr::get_current_device_resource()) const
+  std::unique_ptr<column> operator()(column_view const&,
+                                     column_view const&,
+                                     rmm::cuda_stream_view,
+                                     rmm::mr::device_memory_resource*) const
   {
     CUDF_FAIL("Unsupported type for merge.");
   }

cpp/tests/join/conditional_join_tests.cu

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2019-2020, NVIDIA CORPORATION.
+ * Copyright (c) 2019-2021, NVIDIA CORPORATION.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -44,8 +44,6 @@ constexpr cudf::size_type JoinNoneValue =
 // Common column references.
 const auto col_ref_left_0  = cudf::ast::column_reference(0, cudf::ast::table_reference::LEFT);
 const auto col_ref_right_0 = cudf::ast::column_reference(0, cudf::ast::table_reference::RIGHT);
-const auto col_ref_left_1  = cudf::ast::column_reference(1, cudf::ast::table_reference::LEFT);
-const auto col_ref_right_1 = cudf::ast::column_reference(1, cudf::ast::table_reference::RIGHT);
 
 // Common expressions.
 auto left_zero_eq_right_zero =