fix: warning when building macOS arm64 wheels

When `MACOSX_DEPLOYMENT_TARGET` is not set by the user, cibuildwheel always defaults to `10.9`.
This leads to warning when building arm64 wheels.
This commit removes the warning by setting the default to `11.0` for arm64 builds.

cibuildwheel/macos.py

@@ -207,13 +207,15 @@ def setup_python(
         )
         sys.exit(1)
 
-    # Set MACOSX_DEPLOYMENT_TARGET to 10.9, if the user didn't set it.
-    # PyPy defaults to 10.7, causing inconsistencies if it's left unset.
-    env.setdefault("MACOSX_DEPLOYMENT_TARGET", "10.9")
-
     config_is_arm64 = python_configuration.identifier.endswith("arm64")
     config_is_universal2 = python_configuration.identifier.endswith("universal2")
 
+    # Set MACOSX_DEPLOYMENT_TARGET, if the user didn't set it.
+    # For arm64, the minimal deployment target is 11.0.
+    # On x86_64 (or universal2), use 10.9 as a default.
+    # PyPy defaults to 10.7, causing inconsistencies if it's left unset.
+    env.setdefault("MACOSX_DEPLOYMENT_TARGET", "11.0" if config_is_arm64 else "10.9")
+
     if python_configuration.version not in {"3.6", "3.7"}:
         if config_is_arm64:
             # macOS 11 is the first OS with arm64 support, so the wheels

test/test_macos_archs.py

@@ -66,11 +66,15 @@ def test_cross_compiled_test(tmp_path, capfd, build_universal2):
             "CIBW_BUILD": "cp39-*",
             "CIBW_TEST_COMMAND": '''python -c "import platform; print('running tests on ' + platform.machine())"''',
             "CIBW_ARCHS": "universal2" if build_universal2 else "x86_64 arm64",
+            "CIBW_BUILD_VERBOSITY": "3",
         },
     )
 
     captured = capfd.readouterr()
 
+    assert "[WARNING] MACOSX_DEPLOYMENT_TARGET is set to a lower value" not in captured.out
+    assert "[WARNING] MACOSX_DEPLOYMENT_TARGET is set to a lower value" not in captured.err
+
     if platform.machine() == "x86_64":
         # ensure that tests were run on only x86_64
         assert "running tests on x86_64" in captured.out