[Ada] Crash on named actual in postcondition for generic subprogram

[Ada] Crash on named actual in postcondition for generic subprogram

This patch fixes a crash on compiling the postcondtion for a generic
subprogram, when the postcondition is a call with both positional and
named parameter associations.

2019-07-08  Ed Schonberg  <schonberg@adacore.com>

gcc/ada/

	* sem_ch13.adb (Analyze_Aspect_Specifications): For a
	pre/postcondition of a generic subprogram declaration, do not
	use Relocate_Node on the aspect expression to construct the
	corresponding attribute specification, to prevent tree anomalies
	when the expression is a call with named actual parameters.

gcc/testsuite/

	* gnat.dg/predicate9.adb: New testcase.

From-SVN: r273201