frontend.adb (Frontend): Skip -gnatec=gnat.adc switch, because we've already read...

frontend.adb (Frontend): Skip -gnatec=gnat.adc switch, because we've already read gnat.adc by default.

2017-09-06  Bob Duff  <duff@adacore.com>

	* frontend.adb (Frontend): Skip -gnatec=gnat.adc
	switch, because we've already read gnat.adc by default.

2017-09-06  Bob Duff  <duff@adacore.com>

	* exp_ch5.adb (Get_Default_Iterator): Replace
	"Assert(False)" with "return Iter", because if an iterable
	type is derived from a noniterable one, then we won't find an
	overriding or inherited default iterator.

From-SVN: r251774