[Ada] Use runtime from base compiler during stage1

[Ada] Use runtime from base compiler during stage1

gcc/ada/

	* Make-generated.in: Add rule to copy runtime files needed
	during stage1.
	* raise.c: Remove obsolete symbols used during bootstrap.
	* gcc-interface/Make-lang.in: Do not use libgnat sources during
	stage1.
	(GNAT_ADA_OBJS, GNATBIND_OBJS): Split in two parts, the common
	part and the part only used outside of stage1.
	(ADA_GENERATED_FILES): Add runtime files needed during bootstrap
	when recent APIs are needed.
	(ada/b_gnatb.adb): Remove prerequisite.
	* gcc-interface/system.ads: Remove obsolete entries.