Fix build of universal2 wheels

When building universal2 wheels, we need to set the architectures for
CMake. This was not detected properly before.

setup.py

@@ -4,14 +4,11 @@
 # https://github.com/pybind/cmake_example
 
 import os
-import platform
 from pathlib import Path
-import re
 import subprocess
 import sys
 from pathlib import Path
 
-import setuptools
 from setuptools import Extension, setup
 from setuptools.command.build_ext import build_ext
 
@@ -104,11 +101,9 @@ def build_extension(self, ext: CMakeExtension) -> None:
                 ]
                 build_args += ["--config", cfg]
 
-        if sys.platform.startswith("darwin"):
-            # Cross-compile support for macOS - respect ARCHFLAGS if set
-            archs = re.findall(r"-arch (\S+)", os.environ.get("ARCHFLAGS", ""))
-            if archs:
-                cmake_args += ["-DCMAKE_OSX_ARCHITECTURES={}".format(";".join(archs))]
+        # When building universal2 wheels, we need to set the architectures for CMake.
+        if "universal2" in self.plat_name:
+            cmake_args += ["-DCMAKE_OSX_ARCHITECTURES=arm64;x86_64"]
 
         # Set CMAKE_BUILD_PARALLEL_LEVEL to control the parallel build level
         # across all generators.