add MacOS arm64 wheels

Python 3.8-3.10 only (as was done for SciPy)

use Python 3.9 for the Mac OS builds

arm64 case needs to downloads the arm64 version of libomp
skip universal2 for now until universal2 libomp is available

update MACOSX_DEPLOYMENT_TARGET to 12.0 for arm64
This follows SciPy (scipy/scipy#14688)

.github/workflows/wheel_tests_and_release.yml

@@ -9,8 +9,6 @@ env:
   CIBW_TEST_REQUIRES: "-r requirements/test.txt"
   CIBW_TEST_COMMAND: pytest --pyargs skimage
   CIBW_ENVIRONMENT: PIP_PREFER_BINARY=1
-  # (currently not avaialable for scipy)
-  CIBW_ARCHS_MACOS: x86_64 # TODO: add arm64 universal2
 
 
 jobs:
@@ -104,14 +102,23 @@ jobs:
           path: ./dist/*.whl
 
   build_macos_wheels:
-    name: Build wheels on ${{ matrix.os }}
+    name: Build python ${{ matrix.cibw_python }} ${{ matrix.cibw_arch }} wheels on ${{ matrix.os }}
     runs-on: ${{ matrix.os }}
     strategy:
       fail-fast: false
       matrix:
         os: [macos-latest]
-    env:
-      MACOSX_DEPLOYMENT_TARGET: "10.13"
+        cibw_python: [ "cp37-*", "cp38-*", "cp39-*", "cp310-*" ]
+        # TODO: add "universal2" once a universal2 libomp is available
+        cibw_arch: [ "x86_64", "arm64"]
+        exclude:
+          - os: macos-latest
+            cibw_python: "cp37-*"
+            cibw_arch: arm64
+        #   - os: macos-latest
+        #     cibw_python: "cp37-*"
+        #     cibw_arch: universal2
+
     steps:
       - uses: actions/checkout@v2
         with:
@@ -120,7 +127,7 @@ jobs:
       - uses: actions/setup-python@v2
         name: Install Python
         with:
-          python-version: '3.7'
+          python-version: '3.9'
 
       - name: Install cibuildwheel
         run: |
@@ -134,14 +141,24 @@ jobs:
           # supported macos version is: High Sierra / 10.13. When upgrading
           # this, be sure to update the MACOSX_DEPLOYMENT_TARGET environment
           # variable accordingly. Note that Darwin_17 == High Sierra / 10.13.
-          wget https://packages.macports.org/libomp/libomp-11.0.1_0+universal.darwin_17.i386-x86_64.tbz2 -O libomp.tbz2
+          if [[ "$CIBW_BUILD" == *-macosx_arm64 ]]; then
+              # SciPy requires 12.0 on arm to prevent kernel panics
+              # https://github.com/scipy/scipy/issues/14688
+              # so being conservative, we just do the same here
+              export MACOSX_DEPLOYMENT_TARGET=12.0
+              wget https://packages.macports.org/libomp/libomp-11.0.1_0.darwin_20.arm64.tbz2 -O libomp.tbz2
+          else
+              export MACOSX_DEPLOYMENT_TARGET=10.13
+              wget https://packages.macports.org/libomp/libomp-11.0.1_0+universal.darwin_17.i386-x86_64.tbz2 -O libomp.tbz2
+          fi
           sudo tar -C / -xvjf libomp.tbz2 opt
           python -m cibuildwheel --output-dir dist
         env:
-          CIBW_BUILD: "cp3?-* cp310-*"
-          CIBW_SKIP: "cp36-*"
+          CIBW_BUILD: ${{ matrix.cibw_python }}
+          CIBW_ARCHS_MACOS: ${{ matrix.cibw_arch }}
           CIBW_MANYLINUX_X86_64_IMAGE: manylinux1
           CIBW_MANYLINUX_I686_IMAGE: manylinux1
+          CIBW_TEST_SKIP: "*-macosx_arm64"
           # CIBW_BEFORE_BUILD: pip install certifi numpy==1.19.3
           CC: /usr/bin/clang
           CXX: /usr/bin/clang++
@@ -220,8 +237,6 @@ jobs:
           name: wheels
           path: ./dist/*.whl
 
-
-
   deploy:
     name: Release
     needs: [build_linux_37_and_above_wheels, build_linux_aarch64_wheels, build_macos_wheels, build_windows_wheels]
@@ -252,9 +267,9 @@ jobs:
         run: |
           SK_VERSION=$(git describe --tags)
           python setup.py sdist
-          ls -la ${{ github.workspace }}/dist 
-          # We prefer to release wheels before source because otherwise there is a 
-          # small window during which users who pip install scikit-image will require compilation. 
+          ls -la ${{ github.workspace }}/dist
+          # We prefer to release wheels before source because otherwise there is a
+          # small window during which users who pip install scikit-image will require compilation.
           twine upload ${{ github.workspace }}/dist/*.whl
           twine upload ${{ github.workspace }}/dist/scikit-image-${SK_VERSION:1}.tar.gz
         env: