message: Make is_windows function more robust in build_pip_package.sh
  Fixes #22186#issuecomment-420020276
diff: @@ -43,8 +43,7 @@ function cp_external() {
  PLATFORM="$(uname -s | tr 'A-Z' 'a-z')"
  function is_windows() {
  - # On windows, the shell script is actually running in msys
  - if [[ "${PLATFORM}" =~ (mingw64|msys)_nt* ]]; then
  + if [[ "${PLATFORM}" =~ (cygwin|mingw32|mingw64|msys)_nt* ]]; then
  true
  else
  false
  