Do not silently continue if config.{build,host,gcc} fails

Do not silently continue if config.{build,host,gcc} fails

If config.{build,host,gcc} fails, configure currently silently
continues.  This then makes it much harder than necessary to notice
you made a stupid pasto in config.gcc (and where exactly).

	* configure.ac: If any of the config.* scripts fail, exit 1.
	* configure: Regenerate.

From-SVN: r250507