[Ada] Fix infinite loop in compilation of illegal code

gcc/ada/

	* atree.adb (Rewrite): Fix parent node of shared aspects.
	* atree.ads (Rewrite): Add ??? comment on incorrect
	documentation.
	* einfo-utils.adb (Known_Esize): Fix logic.
	* sem_ch13.adb (Alignment_Check_For_Size_Change,
	Analyze_Attribute_Definition_Clause): Protect against unset
	Size.
4 files changed