config.sh: add custom functions to temporarily pin wheel to 0.31.1

borrowed from https://github.com/python-pillow/pillow-wheels/blob/d5435c9a735bd285297f191703fb2faa4cca8b51/config.sh#L73-L101

config.sh

@@ -26,3 +26,33 @@ function run_tests {
     # Install pre-compiled wheel and run tests against it
     tox --installpkg "${wheel}" -e "${TOXENV}"
 }
+
+# Custom functions to temporarily pin wheel to 0.31.1
+if [ -n "$IS_OSX" ]; then
+    function before_install {
+        brew cask uninstall oclint || true
+        export CC=clang
+        export CXX=clang++
+        get_macpython_environment $MB_PYTHON_VERSION venv
+        source venv/bin/activate
+        pip install --upgrade pip
+        pip install wheel==0.31.1
+    }
+else
+    function build_wheel_cmd {
+        local cmd=${1:-pip_wheel_cmd}
+        local repo_dir=${2:-$REPO_DIR}
+        [ -z "$repo_dir" ] && echo "repo_dir not defined" && exit 1
+        local wheelhouse=$(abspath ${WHEEL_SDIR:-wheelhouse})
+        start_spinner
+        if [ -n "$(is_function "pre_build")" ]; then pre_build; fi
+        stop_spinner
+        if [ -n "$BUILD_DEPENDS" ]; then
+            pip install $(pip_opts) $BUILD_DEPENDS
+        fi
+        /opt/python/cp36-cp36m/bin/pip3 install wheel==0.31.1
+        (cd $repo_dir && $cmd $wheelhouse)
+        pip show wheel
+        repair_wheelhouse $wheelhouse
+    }
+fi