set DECL_SIZE_UNIT for zero-sized fields

Zero-sized fields do not get processed by finish_record_type: they're
removed from the field list before and reinserted after, so their
DECL_SIZE_UNIT remains unset, causing the translation of assignment
statements with use_memset_p, in quite unusual circumstances, to use a
NULL_TREE as the memset length.  This patch sets DECL_SIZE_UNIT for
the zero-sized fields, that don't go through language-independent
layout, in language-specific layout.


for  gcc/ada/ChangeLog

	* gcc-interface/decl.c (components_to_record): Set
	DECL_SIZE_UNIT for zero-sized fields.

From-SVN: r276173

gcc/ada/ChangeLog

+2019-09-26  Alexandre Oliva <oliva@adacore.com>
+
+	* gcc-interface/decl.c (components_to_record): Set
+	DECL_SIZE_UNIT for zero-sized fields.
+
 2019-09-26  Arnaud Charlet  <charlet@adacore.com>
 
 	* osint.adb (OS_Time_To_GNAT_Time): Remove dependency on To_C/To_Ada

gcc/ada/gcc-interface/decl.c

@@ -7928,6 +7928,7 @@ components_to_record (Node_Id gnat_component_list, Entity_Id gnat_record_type,
 
       if (DECL_SIZE (gnu_field) && integer_zerop (DECL_SIZE (gnu_field)))
 	{
+	  DECL_SIZE_UNIT (gnu_field) = size_zero_node;
 	  DECL_FIELD_OFFSET (gnu_field) = size_zero_node;
 	  SET_DECL_OFFSET_ALIGN (gnu_field, BIGGEST_ALIGNMENT);
 	  DECL_FIELD_BIT_OFFSET (gnu_field) = bitsize_zero_node;