{ "for host":
  { "vars": ["ARCH", "HOST_ARCH"]
  , "expression":
    { "type": "singleton_map"
    , "key": "TARGET_ARCH"
    , "value":
      { "type": "var"
      , "name": "HOST_ARCH"
      , "default": {"type": "var", "name": "ARCH"}
      }
    }
  }
, "with fPIC":
  { "doc":
    [ "Transition that enables BUILD_POSITION_INDEPENDENT if config_field"
    , "\"shared\" is not empty."
    ]
  , "expression":
    { "type": "if"
    , "cond": {"type": "FIELD", "name": "shared"}
    , "then":
      { "type": "singleton_map"
      , "key": "BUILD_POSITION_INDEPENDENT"
      , "value": true
      }
    , "else": {"type": "empty_map"}
    }
  }
}