Fix compiler warnings. (dmlc#11226)

Author: trivialfis

src/collective/comm.h

@@ -159,6 +159,7 @@ class Channel {
  public:
   explicit Channel(Comm const& comm, std::shared_ptr<TCPSocket> sock)
       : sock_{std::move(sock)}, comm_{comm} {}
+  virtual ~Channel() = default;
 
   [[nodiscard]] virtual Result SendAll(std::int8_t const* ptr, std::size_t n) {
     Loop::Op op{Loop::Op::kWrite, comm_.Rank(), const_cast<std::int8_t*>(ptr), n, sock_.get(), 0};

src/common/ranking_utils.h

@@ -380,7 +380,6 @@ bool IsBinaryRel(linalg::VectorView<float const> label, AllOf all_of) {
  */
 template <typename AllOf>
 void CheckPreLabels(StringView name, linalg::VectorView<float const> label, AllOf all_of) {
-  auto s_label = label.Values();
   auto is_binary = IsBinaryRel(label, all_of);
   CHECK(is_binary) << name << " can only be used with binary labels.";
 }

src/data/extmem_quantile_dmatrix.cc

@@ -148,17 +148,15 @@ void ExtMemQuantileDMatrix::InitFromCUDA(
 BatchSet<EllpackPage> ExtMemQuantileDMatrix::GetEllpackBatches(Context const *,
                                                                const BatchParam &) {
   common::AssertGPUSupport();
-  auto batch_set =
-      std::visit([this](auto &&ptr) { return BatchSet{BatchIterator<EllpackPage>{ptr}}; },
-                 this->ellpack_page_source_);
+  auto batch_set = std::visit([](auto &&ptr) { return BatchSet{BatchIterator<EllpackPage>{ptr}}; },
+                              this->ellpack_page_source_);
   return batch_set;
 }
 
 BatchSet<EllpackPage> ExtMemQuantileDMatrix::GetEllpackPageImpl() {
   common::AssertGPUSupport();
-  auto batch_set =
-      std::visit([this](auto &&ptr) { return BatchSet{BatchIterator<EllpackPage>{ptr}}; },
-                 this->ellpack_page_source_);
+  auto batch_set = std::visit([](auto &&ptr) { return BatchSet{BatchIterator<EllpackPage>{ptr}}; },
+                              this->ellpack_page_source_);
   return batch_set;
 }
 #endif