[Ada] Unnesting: add a predicate to help expansion of task and protected types

[Ada] Unnesting: add a predicate to help expansion of task and protected types

2018-05-31  Ed Schonberg  <schonberg@adacore.com>

gcc/ada/

	* exp_unst.ads, exp_unst.adb (In_Synchronized_Unit): New predicate to
	mark subprograms that cannot be eliminated because they must be treated
	as reachable from outside the current unit. This includes entry bodies
	and protected operations.

From-SVN: r260994