[Ada] Fix an ICE on instantiated subprogram with -gnatc

[Ada] Fix an ICE on instantiated subprogram with -gnatc

The following should compile quietly:

$ gcc -c p-proc.ads -gnatc

procedure P.Proc is new G;

with Q;

package P is

  generic procedure G;

end P;

with System;
with Unchecked_Conversion;

package Q is

  generic package Inner_G is

    type T is access all Integer;

    function Cnv is new Unchecked_Conversion (System.Address, T);

  end Inner_G;

end Q;

2018-12-11  Eric Botcazou  <ebotcazou@adacore.com>

gcc/ada/

	* gcc-interface/trans.c (elaborate_all_entities_for_package):
	Skip aliasing subprograms.

From-SVN: r266984