protobuf/kokoro/macos/prepare_build_macos_rc

#!/bin/bash
#
# This script sets up a Kokoro MacOS worker for running Protobuf tests

set -eux

##
# Select Xcode version

# Remember to update the Xcode version when Xcode_11.3.app is not available.
# If xcode is not available, it will probably encounter the failure for
# "autom4te: need GNU m4 1.4 or later: /usr/bin/m4"
# go/kokoro/userdocs/macos/selecting_xcode.md for more information.
export DEVELOPER_DIR=/Applications/Xcode_11.3.app/Contents/Developer

##
# Select C/C++ compilers

export CC=gcc
export CXX=g++

##
# Install Tox

if [[ "${KOKORO_INSTALL_TOX:-}" == "yes" ]] ; then
  sudo python3 -m pip install --upgrade pip tox
fi

##
# Install RVM

if [[ "${KOKORO_INSTALL_RVM:-}" == "yes" ]] ; then
  curl -sSL https://rvm.io/mpapis.asc | gpg --import -
  curl -sSL https://rvm.io/pkuczynski.asc | gpg --import -

  # Old OpenSSL versions cannot handle the SSL certificate used by
  # https://get.rvm.io, so as a workaround we download RVM directly from
  # GitHub. See this issue for details: https://github.com/rvm/rvm/issues/5133
  curl -sSL https://raw.githubusercontent.com/rvm/rvm/master/binscripts/rvm-installer | bash -s master --ruby
fi