[Ada] Crash on ignored Ghost expression function

[Ada] Crash on ignored Ghost expression function

This patch updates freezing to ensure that freeze nodes are inserted
into the tree when the entity being frozen is non-Ghost, and the context
is an ignored Ghost spec expression.

2018-12-11  Hristian Kirtchev  <kirtchev@adacore.com>

gcc/ada/

	* exp_util.adb (Insert_Action): Add new formal parameter
	Spec_Expr_OK.
	(Insert_Actions): Add new formal parameter Spec_Expr_OK. Update
	all calls to Insert_Actions where relevant. Honour an insertion
	from a spec expression context when requested by the caller.
	* exp_util.ads (Insert_Action): Add new formal parameter
	Spec_Expr_OK.
	(Insert_Actions): Add new formal parameter Spec_Expr_OK.
	* freeze.adb (Add_To_Result): Force the insertion of the freeze
	node even when the context is a spec expression.

gcc/testsuite/

	* gnat.dg/ghost2.adb, gnat.dg/ghost2.ads: New testcase.

From-SVN: r266996