[Ada] Crash on quantified expression in disabled assertion

[Ada] Crash on quantified expression in disabled assertion

The defining identifier of a quantified expression may be the freeze
point of its type.  If the quantified expression appears in an assertion
that is disavbled, the freeze node for that type may appear in a tree
that will be discarded when the enclosing pragma is elaborated. To
ensure that the freeze node is reachable for subsquent uses we must
generate its freeze node explicitly when the quantified expression is
analyzed.

2019-08-14  Ed Schonberg  <schonberg@adacore.com>

gcc/ada/

	* exp_ch4.adb (Expand_N_Quantified_Expression): Freeze
	explicitly the type of the loop parameter.

gcc/testsuite/

	* gnat.dg/assert2.adb, gnat.dg/assert2.ads: New testcase.

From-SVN: r274456