* decl.c (gnat_to_gnu_entity) <E_Record_Subtype>: Rewrite the handling

	* decl.c (gnat_to_gnu_entity) <E_Record_Subtype>: Rewrite the handling
	of constrained discriminated record subtypes.
	(components_to_record): Declare the type of the variants and of the
	qualified union.
	(build_subst_list): Move around.
	(compute_field_positions): Rename into...
	(build_position_list): ...this.  Return a TREE_VEC.
	(annotate_rep): Adjust for above renaming.
	(build_variant_list): New static function.
	(create_field_decl_from): Likewise.
	(get_rep_part): Likewise.
	(get_variant_part): Likewise.
	(create_variant_part_from): Likewise.
	(copy_and_substitute_in_size): Likewise.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@152272 138bc75d-0d04-0410-961f-82ee72b054a4