[Ada] Crash on precondition involving quantified expression

[Ada] Crash on precondition involving quantified expression

This patch fixes a compiler abort on a precondition whose condition
includes a quantified expression.

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

gcc/ada/

	* sem_util.adb (New_Copy_Tree, Visit_Entity): A quantified
	expression includes the implicit declaration of the loop
	parameter. When a quantified expression is copied during
	expansion, for example when building the precondition code from
	the generated pragma, a new loop parameter must be created for
	the new tree, to prevent duplicate declarations for the same
	symbol.

gcc/testsuite/

	* gnat.dg/predicate12.adb, gnat.dg/predicate12.ads: New
	testcase.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@274449 138bc75d-0d04-0410-961f-82ee72b054a4