Build separate OSX wheels

.github/workflows/wheels.yml

@@ -15,7 +15,7 @@ jobs:
     runs-on: macos-latest
     strategy:
       matrix:
-        python: [3.8, 3.9, "3.10", 3.11]
+        python: [3.9, "3.10", 3.11, 3.12]
     steps:
       - name: Checkout
         uses: actions/checkout@v4
@@ -31,11 +31,25 @@ jobs:
           pip install --upgrade pip build
       - name: Build Wheel
         run: |
+          export PLAT="arm64"
+          export _PYTHON_HOST_PLATFORM="macosx-11.0-arm64"
+          export OLDARCHFLAGS=$ARCHFLAGS
+          export ARCHFLAGS+="-arch arm64"
+          python -m build --wheel
+          export PLAT="x86_64"
+          export _PYTHON_HOST_PLATFORM="macosx-11.0-x86_64"
+          export CFLAGS+=" -arch x86_64"
+          export CXXFLAGS+=" -arch x86_64"
+          export ARCHFLAGS=$OLDARCHFLAGS
+          export ARCHFLAGS+=" -arch x86_64"
+          export CPPFLAGS+=" -arch x86_64"
+          export LDFLAGS+=" -arch x86_64"
           python -m build --wheel
       - name: Delocate to bundle dynamic libs
         run: |
           pip install delocate
-          delocate-wheel -v dist/*.whl
+          delocate-wheel -v dist/msprime-*arm64.whl
+          delocate-wheel -v dist/msprime-*x86_64.whl
       - name: Upload Wheels
         uses: actions/upload-artifact@v4
         with:
@@ -49,7 +63,7 @@ jobs:
         uses: actions/checkout@v4
         with:
             submodules: true
-      - name: Set up Python 3.8
+      - name: Set up Python 3.9
         uses: actions/setup-python@v5
         with:
           python-version: 3.9