enable cpp kernl building

Author: Valentine233

setup.py

@@ -385,19 +385,16 @@ def get_extensions():
         extra_compile_args["cxx"].extend(
             ["-O3" if not debug_mode else "-O0", "-fdiagnostics-color=always"]
         )
-
-        # TODO(future PR): make this work without using `TORCH_VERSION_AT_LEAST_2_7`,
-        # because we should not be using anything from `torchao` to build `torchao`.
-        # if use_cpu_kernels and is_linux and TORCH_VERSION_AT_LEAST_2_7:
-        #     if torch._C._cpu._is_avx512_supported():
-        #         extra_compile_args["cxx"].extend(
-        #             [
-        #                 "-DCPU_CAPABILITY_AVX512",
-        #                 "-march=native",
-        #                 "-mfma",
-        #                 "-fopenmp",
-        #             ]
-        #         )
+        if use_cpu_kernels and is_linux and hasattr(torch._C._cpu, "_is_avx512_supported"):
+            if torch._C._cpu._is_avx512_supported():
+                extra_compile_args["cxx"].extend(
+                    [
+                        "-DCPU_CAPABILITY_AVX512",
+                        "-march=native",
+                        "-mfma",
+                        "-fopenmp",
+                    ]
+                )
 
         if debug_mode:
             extra_compile_args["cxx"].append("-g")