[Ada] Suppress warnings in generic instantiations with pragma Warnings

[Ada] Suppress warnings in generic instantiations with pragma Warnings

Warnings issued by GNAT or GNATprove inside generic instantiations can
now be suppressed by using pragma Warnings Off/On around the instance.
This has mostly an effect on GNATprove, since GNAT typically does not
issue warnings on instantiations, only on the generic code itself.

2019-07-03  Yannick Moy  <moy@adacore.com>

gcc/ada/

	* erroutc.adb (Sloc_In_Range): New function to determine whether
	the range of a pragma Warnings covers a location, taking
	instantiations into account.

From-SVN: r272985