[Ada] Extend -gnatw.z warning to array types

[Ada] Extend -gnatw.z warning to array types

The -gnatw.z switch causes the compiler to issue a warning on record
types subject to both an alignment clause and a size clause, when the
specified size is not a multiple of the alignment in bits, because this
means that the Object_Size will be strictly larger than the specified
size.

It makes sense to extend this warning to array types, but not to the
cases of bit-packed arrays where the size is not a multiple of storage
unit and the specified alignment is the minimum one, because there would
be no way to get rid of it apart from explicitly silencing it.

The compiler must issue the warning:

p.ads:5:03: warning: size is not a multiple of alignment for "Triplet"
p.ads:5:03: warning: size of 24 specified at line 4
p.ads:5:03: warning: Object_Size will be increased to 32

on the following package:

package P is

  type Triplet is new String (1 .. 3);
  for Triplet'Size use 24;
  for Triplet'Alignment use 4;

  type Arr is array (1 .. 7) of Boolean;
  pragma Pack (Arr);
  for Arr'Size use 7;
  for Arr'Alignment use 1;

end P;

2019-07-03  Eric Botcazou  <ebotcazou@adacore.com>

gcc/ada/

	* doc/gnat_ugn/building_executable_programs_with_gnat.rst
	(Warning message control): Document that -gnatw.z/Z apply to
	array types.
	* freeze.adb (Freeze_Entity): Give -gnatw.z warning for array
	types as well, but not if the specified alignment is the minimum
	one.
	* gnat_ugn.texi: Regenerate.

From-SVN: r272971