Add MUSL linux build (#272)

* Add MUSL linux build

update workflow to add a musllinux build

* Add new test target based on the alpine linux image wit python 3.9 installed. However some extras are needed for building. This is wat we want to avoid in all other containers.

.github/workflows/ci.yml

@@ -95,3 +95,21 @@
               /opt/python/${{ matrix.PYTHON.VERSION }}/bin/python -m venv .venv;
               .venv/bin/pip install -U tox;
               .venv/bin/tox -e ${{ matrix.PYTHON.TOXENV }};"
+
+  musllinux:
+    name: "${{ matrix.PYTHON.TOXENV }} on musllinux"
+    runs-on: ubuntu-20.04
+    strategy:
+      matrix:
+        PYTHON:
+          - {VERSION: "3.9", TOXENV: "py39"}
+    steps:
+      - uses: actions/checkout@v2.3.5
+      - uses: docker://registry.hub.docker.com/library/python:3.9-alpine
+        with:
+          args: |
+              sh -c "set -xe;
+              python -m venv .venv;
+              apk add gcc py3-wheel libc-dev libffi-dev alpine-sdk;
+              .venv/bin/pip install -U tox;
+              .venv/bin/tox -e ${{ matrix.PYTHON.TOXENV }};"

.github/workflows/wheel-builder.yml

@@ -16,6 +16,7 @@
         CONTAINER:
           - {IMAGE: "pyca/cryptography-manylinux1:x86_64", NAME: "manylinux1"}
           - {IMAGE: "pyca/cryptography-manylinux2010:x86_64", NAME: "manylinux2010"}
+          - {IMAGE: "pyca/cryptography-musllinux_1_1:x86_64", NAME: "cryptography-musllinux_1_1"}
     name: "${{ matrix.PYTHON.ABI_VERSION }} ${{ matrix.CONTAINER.NAME }}"
     container: ${{ matrix.CONTAINER.IMAGE }}
     steps: