Install libffi-dev on Linux wheel builds

Author: sethmlarson

.github/workflows/ci.yml

@@ -113,6 +113,7 @@ jobs:
         env:
           CIBW_BUILD: cp27-${{ matrix.name }}* cp35-${{ matrix.name }}* pp*-${{ matrix.name }}*
           CIBW_ARCHS_LINUX: auto aarch64
+          CIBW_BEFORE_BUILD_LINUX: yum install -y libffi-devel
       - uses: actions/upload-artifact@v2
         with:
           name: wheels-${{ matrix.name }}