message: allow to override ZLIB_HOME on macOS
  Summary: On macOS, users can install homebrew in their home directory, and thus they will need to provide `-DZLIB_HOME`. Unfortunately, that doesn't work as we override that. Let's fix it.
diff: @@ -63,7 +63,7 @@ macro(add_dependent_packages_for_redex)
  set(REDEX_JSONCPP_LIBRARY ${JSONCPP_LIBRARY})
  endif()
  - if (APPLE)
  + if (APPLE AND (NOT ZLIB_HOME))
  #Static library is not installed on default path in MacOS because it conflicts with Xcode Version
  set(ZLIB_HOME "/usr/local/opt/zlib/")
  endif ()
  