[Ada] Support aspect Relaxed_Initialization and attribute Initialized

[Ada] Support aspect Relaxed_Initialization and attribute Initialized

2020-06-15  Piotr Trojanek  <trojanek@adacore.com>

gcc/ada/

	* aspects.ads (Aspect_Id): Add Aspect_Relaxed_Initialization.
	(Implementation_Defined_Aspect): Add new aspect.
	(Aspect_Argument): Add new aspect with Optional_Expression
	argument.
	(Is_Representation_Aspect): Add new aspect as a
	non-representation one.
	(Aspect_Names): Add name for the new aspect.
	(Aspect_Delay): Add new aspect as a non-delayed one.
	* sem_ch3.adb: Minor reformatting.
	* einfo.ads, einfo.adb (Is_Relaxed_Initialization_State): New
	query; reuses existing code for querying abstract state options.
	* exp_attr.adb (Expand_N_Attribute_Reference): For now ignore
	attribute 'Initialized.
	* sem_attr.adb (Analyze_Attribute_Old_Result): Allow attribute
	'Result to be used in the aspect Relaxed_Initialization
	expression.
	(Analyze_Attribute): Analyze attribute 'Initialized; based on
	existing code for attribute 'Valid_Scalars.
	(Eval_Attribute): Do not expect attribute 'Initialized, just
	like attribute 'Valid_Scalars is not expected.
	* sem_ch13.adb (Analyze_Aspect_Relaxed_Initialization): New
	routine.
	(Analyze_Aspect_Specifications): Analyze new aspect in a
	dedicated routine.
	(Check_Aspect_At_Freeze_Point): Do not expect new aspect.
	* sem_prag.adb (Analyze_Abstract_State): Support option
	Relaxed_Initialization on abstract states.
	* sem_util.ads, sem_util.adb (Has_Relaxed_Initialization): New
	query for the GNATprove backend.
	* snames.ads-tmpl (Snames): Add Name_Ids for the new aspect and
	attribute; add an Attribute_Id for the new attribute.