[Ada] Extend pragma Implicit_Packing for records to composite components

[Eric Botcazou]

The implementation of pragma Implicit_Packing for record types was restricted
to scalar components, i.e. it gave up as soon as there was one non-scalar
component in the record type.  This change extends it to all the other kinds
of components, at least if they are small.

The following package must compile quietly:

pragma Implicit_Packing;

package P is

  type Rec1 is record
    B : Boolean;
  end record;
  for Rec1'Size use 1;

  type Rec2 is record
    B : Boolean;
    R : Rec1;
  end record;
  for Rec2'Size use 2;

  type Rec3 is record
    B : Boolean;
    R : Rec2;
  end record;
  for Rec3'Size use 3;

end P;


Tested on x86_64-suse-linux, applied on the mainline.


2016-05-16  Eric Botcazou  <ebotcazou@adacore.com>

	* freeze.adb (Freeze_Record_Type): Extend pragma Implicit_Packing to
	components of any elementary types and of composite types.

-- 
Eric Botcazou
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