The compiler crashes processing an internally generated cloned tree that
has a subprogram call with a named actual parameter.

2019-08-21  Javier Miranda  <miranda@adacore.com>

gcc/ada/

	* sem_util.adb (Update_Named_Associations): Update
	First_Named_Actual when the subprogram call has a single named
	actual.

gcc/testsuite/

	* gnat.dg/implicit_param.adb, gnat.dg/implicit_param_pkg.ads:
	New testcase.

From-SVN: r274776