[Ada] Bad access checks on if/case expression as actual

[Ada] Bad access checks on if/case expression as actual

2020-06-15  Justin Squirek  <squirek@adacore.com>

gcc/ada/

	* exp_ch4.adb (Expand_N_Case_Expression): Set default value for
	Target to silence potential warnings.
	(Expand_N_If_Expression): Add calculation to check when the if
	expression is used directly in the context of an actual of an
	anonymous access type and add a special path to force expansion
	of the if expression in this case.
	* exp_ch6.adb (Expand_Branch): Generate an assignment to the
	level temporary for a given branch.
	(Expand_Call_Helper): Add expansion to allow for creating a
	temporary to store associated accessiblity levels on each branch
	of the conditional expression.  Also perform expansion of
	function calls into expressions with actions, and fixup
	references to N with Call_Node.
	(Insert_Level_Assign): Move through nested conditional
	expressions to each branch.
	* sem_util.ads, sem_util.adb (Is_Anonymous_Access_Actual): Added
	to detect when to force expansion of if expressions.