[major] fix M_LOG2E missing on Windows

csrc/block_sparse_attn/flash_api.cpp

@@ -28,6 +28,10 @@ using namespace pytorch_compat;
 #include "src/flash.h"
 #include "src/static_switch.h"
 
+#ifndef M_LOG2E
+#define M_LOG2E 1.4426950408889634074
+#endif
+
 #define CHECK_DEVICE(x) TORCH_CHECK(x.is_cuda(), #x " must be on CUDA")
 #define CHECK_SHAPE(x, ...) TORCH_CHECK(x.sizes() == torch::IntArrayRef({__VA_ARGS__}), #x " must have shape (" #__VA_ARGS__ ")")
 #define CHECK_CONTIGUOUS(x) TORCH_CHECK(x.is_contiguous(), #x " must be contiguous")