[Ada] Spurious error on instantiations with Taft_Amendment types and tasks

[Ada] Spurious error on instantiations with Taft_Amendment types and tasks

2020-06-09  Ed Schonberg  <schonberg@adacore.com>

gcc/ada/

	* exp_ch9.adb (Build_Master_Renaming): Make name in renaming
	declaration unique by adding a numeric suffix, to prevent
	accidental name conflict when several instantiations of a
	package containing an access_to_incomplete type that designate
	tasks appear in the same scope.