[Ada] Missing accessibility checks on conditionals

[Ada] Missing accessibility checks on conditionals

2019-12-13  Justin Squirek  <squirek@adacore.com>

gcc/ada/

	* sem_res.adb (Resolve_Allocator): Add calls to
	Check_Cond_Expr_Accessibility when a conditional expression is
	found.
	(Check_Allocator_Discrim_Accessibility_Exprs): Created to
	recursively traverse a potentially compound conditional
	expression and perform accessibility checks for each
	alternative.
	* sem_util.adb (Dynamic_Accessibility_Level): Avoid use of
	original node of the expression in question so we can handle
	dynamic accessibility in the limited case of a constant folded
	conditional expression.

From-SVN: r279342