fix: guard cuda_bf16.h with __CUDA_ARCH__

dsv4/kernels/attention/fmha_sm100.cuh

@@ -30,9 +30,15 @@
 #pragma once
 
 #include <cuda_runtime.h>
-#include <cuda_bf16.h>
 #include <cstdint>
 
+// __nv_bfloat16 is a built-in type on CUDA 13+
+// cuda_bf16.h may have C++17 compatibility issues with some CUDA versions;
+// only include it in device code where it's guaranteed to work.
+#if defined(__CUDA_ARCH__)
+#include <cuda_bf16.h>
+#endif
+
 // CUTLASS C++ includes (CUDA device code only)
 #if defined(__CUDA_ARCH__)
 #include <cutlass/cutlass.h>