[Fix] fix fa3 build at cu118 (#5036)

sgl-kernel/cmake/utils.cmake

@@ -0,0 +1,21 @@
+# Adapt from: https://github.com/neuralmagic/vllm-flash-attention/blob/main/cmake/utils.cmake
+#
+# Clear all `-gencode` flags from `CMAKE_CUDA_FLAGS` and store them in
+# `CUDA_ARCH_FLAGS`.
+#
+# Example:
+#   CMAKE_CUDA_FLAGS="-Wall -gencode arch=compute_70,code=sm_70 -gencode arch=compute_75,code=sm_75"
+#   clear_cuda_arches(CUDA_ARCH_FLAGS)
+#   CUDA_ARCH_FLAGS="-gencode arch=compute_70,code=sm_70;-gencode arch=compute_75,code=sm_75"
+#   CMAKE_CUDA_FLAGS="-Wall"
+#
+macro(clear_cuda_arches CUDA_ARCH_FLAGS)
+    # Extract all `-gencode` flags from `CMAKE_CUDA_FLAGS`
+    string(REGEX MATCHALL "-gencode arch=[^ ]+" CUDA_ARCH_FLAGS
+      ${CMAKE_CUDA_FLAGS})
+
+    # Remove all `-gencode` flags from `CMAKE_CUDA_FLAGS` since they will be modified
+    # and passed back via the `CUDA_ARCHITECTURES` property.
+    string(REGEX REPLACE "-gencode arch=[^ ]+ *" "" CMAKE_CUDA_FLAGS
+      ${CMAKE_CUDA_FLAGS})
+endmacro()