[Ada] Vectors: spurious error in -gnatwE mode

[Ada] Vectors: spurious error in -gnatwE mode

This patch fixes a bug in which if Ada.Containers.Vectors is instantiated with
an Index_Type such that Index_Type'Base'Last is less than Count_Type'Last, and
the -gnatwE switch is used, the compiler gives spurious error messages.

The following test should compile quietly with -gnatwE:

gnatmake short_vectors.ads -gnatwa -gnatwE -gnatf

with Ada.Containers.Vectors;
package Short_Vectors is

   type Index_Type is range 1 .. 256;

   package Map_Pkg is new Ada.Containers.Vectors
     (Index_Type => Index_Type,
      Element_Type => Integer);

end Short_Vectors;

2018-05-23  Bob Duff  <duff@adacore.com>

gcc/ada/

	* libgnat/a-convec.adb: (Insert, Insert_Space): Suppress warnings. The
	code in question is not reachable in the case where Count_Type'Last is
	out of range.

From-SVN: r260590