[Ada] Do not propagate Object_Size onto Size for composite types

[Ada] Do not propagate Object_Size onto Size for composite types

2019-12-18  Eric Botcazou  <ebotcazou@adacore.com>

gcc/ada/

	* layout.adb (Layout_Type): In the case of composite types, do
	not copy the Esize onto the RM_Size if the latter is not set.
	* gcc-interface/decl.c (gnat_to_gnu_entity) <E_Record_Type>:
	Also cap the alignment if an Object_Size clause has been
	specified.  Pass VAR_DECL in the call to validate_size for the
	Esize of a type.
	(validate_size): Be prepared to give an error on an Object_Size
	clause.

From-SVN: r279507