ada: Unsigned_Base_Range aspect

ada: Unsigned_Base_Range aspect

This patch adds support for a new GNAT aspect/pragma for integer
type definitions to explicitly enforce the use of an unsigned
base type.

gcc/ada/ChangeLog:

	* aspects.ads (Aspect_Unsigned_Base_Range): New aspect.
	* checks.adb (Determine_Range): Handle types with unsigned base range aspect.
	(Enable_Overflow_Check): ditto
	(Apply_Arithmetic_Overflow_Strict): ditto
	* debug.adb (d_o): Document new usage.
	* einfo.ads (Has_Unsigned_Base_Range_Aspect): New flag.
	* exp_attr.adb (Expand_N_Attribute_Reference): No action since
	it has been already handled at this stage.
	* exp_ch4.adb (Expand_N_Op_Add): Generate aritmetic overflow check on
	unsigned base range type operands.
	(Expand_N_Op_Subtract): ditto
	(Expand_N_Op_Multiply): ditto
	(Expand_N_Op_Minus): ditto
	* gen_il-fields.ads (Has_Unsigned_Base_Range_Aspect): New flag.
	* gen_il-gen-gen_entities.adb (Has_Unsigned_Base_Range_Aspect): New flag.
	* gen_il-internals.adb (Has_Unsigned_Base_Range_Aspect): New flag.
	* gnat1drv.adb (Adjust_Global_Switches): Handle -gnatd_o
	* par-prag.adb (Pragma_Unsigned_Base_Range): No action since it will
	be entirely handled by the semantic analyzer.
	* rtsfind.ads (RE_Id): Add RE_Uns_[Add|Subtract|Multiply]_With_ Ovflo_Check
	* sem_attr.ads (Attribute_Unsigned_Base_Range): Added to the set of
	implementation defined attributes.
	* sem_attr.adb (Analyze_Attribute): Analyze attribute Unsigned_Base_Range.
	(Eval_Attribute): Evaluate attribute Unsigned_Base_Range.
	* sem_ch13.adb (Analyze_One_Aspect): Defer checks for this aspect to
	the analysis of the corresponding pragma.
	* sem_ch3.ads (Unsigned_Base_Range_Type_Declaration): New subprogram.
	* sem_ch3.adb (Build_Derived_Numeric_Type): Inherit flag
	Has_Unsigned_Base_Range_Aspect.
	(Unsigned_Base_Range_Type_Declaration): New subprogram.
	(Has_Pragma_Unsigned_Base_Range): New subprogram.
	* sem_prag.adb (Analyze_Pragma): Handle Pragma_Unsigned_Base_Range.
	* snames.adb-tmpl (Get_Pragma_Id): Handle Name_Unsigned_Base_Range.
	(Is_Pragma_Name): ditto.
	* snames.ads-tmpl (Name_Unsigned_Base_Range): New name.
	(Attribute_Unsigned_Base_Range): New attribute.
	(Pragma_Unsigned_Base_Range): New pragma.
	* libgnat/s-aridou.ads (Add_With_Ovflo_Check): New routine for Double_Uns.
	(Subtract_With_Ovflo_Check): ditto.
	(Multiply_With_Ovflo_Check): ditto.
	* libgnat/s-aridou.adb (Add_With_Ovflo_Check): ditto.
	(Subtract_With_Ovflo_Check): ditto.
	(Multiply_With_Ovflo_Check): ditto.
	* libgnat/s-arit64.ads (Uns_Add_With_Ovflo_Check64): New subprogram.
	(Uns_Subtract_With_Ovflo_Check64): ditto.
	(Uns_Multiply_With_Ovflo_Check64): ditto.
	* libgnat/s-arit64.adb (Uns_Add_With_Ovflo_Check64): New subprogram.
	(Uns_Subtract_With_Ovflo_Check64): ditto.
	(Uns_Multiply_With_Ovflo_Check64): ditto.
	* libgnat/s-arit128.ads (Uns_Add_With_Ovflo_Check128): New subprogram.
	(Uns_Subtract_With_Ovflo_Check128): ditto.
	(Uns_Multiply_With_Ovflo_Check128): ditto.
	* libgnat/s-arit128.adb (Uns_Add_With_Ovflo_Check128): New subprogram.
	(Uns_Subtract_With_Ovflo_Check128): ditto.
	(Uns_Multiply_With_Ovflo_Check128): ditto.
	* doc/gnat_rm/gnat_language_extensions.rst: Document unsigned
	base range.
	* gnat_rm.texi: Regenerate.
	* gnat_ugn.texi: Regenerate.