[Ada] Crash on entry in generic with dynamic elaboration checks

[Ada] Crash on entry in generic with dynamic elaboration checks

This patch modifies the set of attributes that applies to entries and
entry families to include elaboration entities used by the
access-before-elaboration mechanism.

2018-08-21  Hristian Kirtchev  <kirtchev@adacore.com>

gcc/ada/

	* einfo.adb (Elaboration_Entity): Include entries and entry
	families in the set of legal entities.
	(Elaboration_Entity_Required): Include entries and entry
	families in the set of legal entities.
	(Set_Elaboration_Entity): Include entries and entry families in
	the set of legal entities.
	(Set_Elaboration_Entity_Required): Include entries and entry
	families in the set of legal entities.
	(Write_Field13_Name): Update the output of attribute
	Elaboration_Entity.
	* einfo.ads: Attributes Elaboration_Entity and
	Elaboration_Entity_Required now apply to entries and entry
	families.

gcc/testsuite/

	* gnat.dg/elab6.adb, gnat.dg/elab6.ads, gnat.dg/elab6_pkg.adb,
	gnat.dg/elab6_pkg.ads: New testcase.

From-SVN: r263712