Select xcode 12.2

Change-Id: I00a8afc652a3fcfaa371a8d92f2f06667b5ab644
diff --git a/kokoro/build.py b/kokoro/build.py
index fde76e7..f0091eb 100755
--- a/kokoro/build.py
+++ b/kokoro/build.py
@@ -71,6 +71,7 @@
     env.update({
         'CC': ' '.join(['cc'] + cflags + ldflags),
         'CXX': ' '.join(['c++'] + cflags + ldflags),
+        'MACOSX_DEPLOYMENT_TARGET': MAC_MIN_VERSION,
     })
 
     subprocess.check_call(config_cmd, cwd=build_dir, env=env)
diff --git a/kokoro/kokoro_build.sh b/kokoro/kokoro_build.sh
index 5173d01..7f53ba2 100755
--- a/kokoro/kokoro_build.sh
+++ b/kokoro/kokoro_build.sh
@@ -7,6 +7,12 @@
 OUT="${KOKORO_ARTIFACTS_DIR}/out"
 PYTHON_SRC=${KOKORO_ARTIFACTS_DIR}/git/cpython3
 
+
+if [ "$(uname)" == "Darwin" ]; then
+    # http://g3doc/devtools/kokoro/g3doc/userdocs/macos/selecting_xcode
+    sudo xcode-select -s /Applications/Xcode_12.2.app/Contents/Developer
+fi
+
 BASEDIR=$(dirname "$0")
 
 python3 --version