[Ada] Aspect/pragma Secondary_Stack_Size can evaluate non-literals as zero

[Ada] Aspect/pragma Secondary_Stack_Size can evaluate non-literals as zero

This patch fixes the problem of aspect/pragma Secondary_Stack_Size expressions
with non-literals evaluating as zero in static secondary stacks allocations.
The aspect Secondary_Stack_Size is now converted to a pragma instead of an
attribute as the attribute does not have visibility on the discriminant.
Additionally, the discriminant of the corresponding record type is now
referenced if the pragma expression contains a discriminant.

No simple test available as the problem only impacts programs when
System.Parameters.Sec_Stack_Dynamic = False

2018-01-11  Patrick Bernardi  <bernardi@adacore.com>

gcc/ada/

	* exp_ch9.adb (Expand_N_Task_Type_Declaration): Simplified
	Secondary_Stack_Size handling as a pragma is now generated for the
	corresponding aspect instead of an attribute.  Pragma expression is
	relocated instead of evaluated. Discriminant of the corresponding
	record type is referenced rather than the type discriminant.
	(Create_Secondary_Stack_For_Task, Make_Task_Create_Call): Update
	Secondary_Stack_Size rep item checks to only look for the pragma rep.
	* sem_ch13.adb (Analyze_One_Aspect): Transform
	Aspect_Secondary_Stack_Size into a pragma instead of an attribute
	because the attribute does not have visibility on a task type's
	discriminants when the type's definition is expanded.
	(Analyze_Attribute_Definition_Clause): Remove handling of
	Attribute_Secondary_Stack_Size.
	* snames.adb-tmpl, snames.ads-tmpl: Remove
	Attribute_Secondary_Stack_Size, no longer used.

From-SVN: r256488