better error message

solution/reduction/reduction.cu

 #include <cstdio>
 #include <algorithm>
 
+#if defined(__CUDA_ARCH__) && __CUDA_ARCH__ < 600
+    #error "This code must be compiled with the -arch=native flag (or -arch=sm_80 for A100)!"
+#endif
+
 constexpr int TPB = 1024;
 
 

tasks/reduction/reduction.cu

 #include <cstdio>
 #include <algorithm>
 
+#if defined(__CUDA_ARCH__) && __CUDA_ARCH__ < 600
+    #error "This code must be compiled with the -arch=native flag (or -arch=sm_80 for A100)!"
+#endif
+
 constexpr int TPB = 1024;