[Ada] Fix PR bootstrap/109510

[Eric Botcazou via Gcc-patches]

This is the build failure of the Ada runtime for Aarch64 targets.  The Aarch64 
back-end now asserts that the main variant of scalar types has TYPE_USER_ALIGN 
cleared, and that's not the case for scalar types declared with a confirming 
alignment clause in Ada.

Tested on Aarch64/Linux by Richard S. (thanks!) and on x86-64/Linux by me, and 
applied on the mainline.


2023-04-14  Eric Botcazou  <ebotca...@adacore.com>

        PR bootstrap/109510
        * gcc-interface/decl.cc (gnat_to_gnu_entity) <types>: Reset align
        to zero if its value is equal to TYPE_ALIGN and the type is scalar.
        Set TYPE_USER_ALIGN on the type only if align is positive.

-- 
Eric Botcazou
diff --git a/gcc/ada/gcc-interface/decl.cc b/gcc/ada/gcc-interface/decl.cc
index d24adf33601..851a6745f77 100644
--- a/gcc/ada/gcc-interface/decl.cc
+++ b/gcc/ada/gcc-interface/decl.cc
@@ -4364,13 +4364,17 @@ gnat_to_gnu_entity (Entity_Id gnat_entity, tree gnu_expr, bool definition)
       /* If the alignment has not already been processed and this is not
 	 an unconstrained array type, see if an alignment is specified.
 	 If not, we pick a default alignment for atomic objects.  */
-      if (align != 0 || TREE_CODE (gnu_type) == UNCONSTRAINED_ARRAY_TYPE)
+      if (align > 0 || TREE_CODE (gnu_type) == UNCONSTRAINED_ARRAY_TYPE)
 	;
       else if (Known_Alignment (gnat_entity))
 	{
 	  align = validate_alignment (Alignment (gnat_entity), gnat_entity,
 				      TYPE_ALIGN (gnu_type));
 
+	  /* Treat confirming clauses on scalar types like the default.  */
+	  if (align == TYPE_ALIGN (gnu_type) && !AGGREGATE_TYPE_P (gnu_type))
+	    align = 0;
+
 	  /* Warn on suspiciously large alignments.  This should catch
 	     errors about the (alignment,byte)/(size,bit) discrepancy.  */
 	  if (align > BIGGEST_ALIGNMENT && Has_Alignment_Clause (gnat_entity))
@@ -4666,7 +4670,7 @@ gnat_to_gnu_entity (Entity_Id gnat_entity, tree gnu_expr, bool definition)
 	    TYPE_BY_REFERENCE_P (gnu_type) = 1;
 
 	  /* Record whether an alignment clause was specified.  */
-	  if (Present (Alignment_Clause (gnat_entity)))
+	  if (align > 0 && Present (Alignment_Clause (gnat_entity)))
 	    TYPE_USER_ALIGN (gnu_type) = 1;
 
 	  /* Record whether a pragma Universal_Aliasing was specified.  */