2017-07-06  Olivier Hainque  <hainque@adacore.com>

        * gcc.c (spec_undefvar_allowed): New global.
        (process_command): Set to true when running for --version or --help
        alone, or together.
        (getenv_spec_function): When the variable is not defined, use the
        variable name as the variable value if we're allowed not to issue
        a fatal error.

From-SVN: r250027