Fix MSVC unused variable warnerr

Author: gonidelis

cub/test/catch2_test_device_histogram_env_api.cu

@@ -85,8 +85,8 @@ C2H_TEST("cub::DeviceHistogram::MultiHistogramEven accepts env with stream (1D)"
 {
   // example-begin multi-histogram-even-1d-env
   // 4-channel RGBA pixels, histogram 3 active channels
-  constexpr int NUM_CHANNELS        = 4;
-  constexpr int NUM_ACTIVE_CHANNELS = 3;
+  [[maybe_unused]] constexpr int NUM_CHANNELS        = 4;
+  [[maybe_unused]] constexpr int NUM_ACTIVE_CHANNELS = 3;
 
   // clang-format off
   // 2 pixels: (R=0, G=2, B=1, A=255), (R=3, G=4, B=2, A=128)
@@ -137,8 +137,8 @@ C2H_TEST("cub::DeviceHistogram::MultiHistogramEven accepts env with stream (2D)"
 {
   // example-begin multi-histogram-even-2d-env
   // 4-channel RGBA pixels, histogram 3 active channels, 2D region
-  constexpr int NUM_CHANNELS        = 4;
-  constexpr int NUM_ACTIVE_CHANNELS = 3;
+  [[maybe_unused]] constexpr int NUM_CHANNELS        = 4;
+  [[maybe_unused]] constexpr int NUM_ACTIVE_CHANNELS = 3;
 
   // 2 rows, 2 pixels per row, with row stride = 2 pixels * 4 channels * 1 byte = 8 bytes
   // Row 0: (R=0, G=2, B=1, A=255), (R=3, G=4, B=2, A=128)
@@ -199,8 +199,8 @@ C2H_TEST("cub::DeviceHistogram::MultiHistogramRange accepts env with stream (1D)
 {
   // example-begin multi-histogram-range-1d-env
   // 4-channel RGBA pixels, histogram 3 active channels
-  constexpr int NUM_CHANNELS        = 4;
-  constexpr int NUM_ACTIVE_CHANNELS = 3;
+  [[maybe_unused]] constexpr int NUM_CHANNELS        = 4;
+  [[maybe_unused]] constexpr int NUM_ACTIVE_CHANNELS = 3;
 
   // 2 pixels: (R=0, G=2, B=1, A=255), (R=3, G=4, B=2, A=128)
   auto d_samples = thrust::device_vector<unsigned char>{0, 2, 1, 255, 3, 4, 2, 128};
@@ -256,8 +256,8 @@ C2H_TEST("cub::DeviceHistogram::MultiHistogramRange accepts env with stream (2D)
 {
   // example-begin multi-histogram-range-2d-env
   // 4-channel RGBA pixels, histogram 3 active channels, 2D region
-  constexpr int NUM_CHANNELS        = 4;
-  constexpr int NUM_ACTIVE_CHANNELS = 3;
+  [[maybe_unused]] constexpr int NUM_CHANNELS        = 4;
+  [[maybe_unused]] constexpr int NUM_ACTIVE_CHANNELS = 3;
 
   // 2 rows, 2 pixels per row
   // Row 0: (R=0, G=2, B=1, A=255), (R=3, G=4, B=2, A=128)