[Ada] Create explicit ghost mirror unit for big integers

gcc/ada/

	* Makefile.rtl: Add unit.
	* libgnat/a-nbnbin__ghost.adb: Move...
	* libgnat/a-nbnbig.adb: ... here. Mark ghost as ignored.
	* libgnat/a-nbnbin__ghost.ads: Move...
	* libgnat/a-nbnbig.ads: ... here.  Add comment for purpose of
	this unit. Mark ghost as ignored.
	* libgnat/s-widthu.adb: Use new unit.
	* sem_aux.adb (First_Subtype): Adapt to the case of a ghost type
	whose freeze node is rewritten to a null statement.

1 files changed, 9 insertions, 1 deletions

diff --git a/gcc/ada/sem_aux.adb b/gcc/ada/sem_aux.adb
index dcced7e..e1bcf53 100644
--- a/gcc/ada/sem_aux.adb
+++ b/gcc/ada/sem_aux.adb
@@ -336,10 +336,18 @@ package body Sem_Aux is
 
    function First_Subtype (Typ : Entity_Id) return Entity_Id is
       B   : constant Entity_Id := Base_Type (Typ);
-      F   : constant Node_Id   := Freeze_Node (B);
+      F   : Node_Id := Freeze_Node (B);
       Ent : Entity_Id;
 
    begin
+      --  The freeze node of a ghost type might have been rewritten in a null
+      --  statement by the time gigi calls First_Subtype on the corresponding
+      --  type.
+
+      if Nkind (F) = N_Null_Statement then
+         F := Original_Node (F);
+      end if;
+
       --  If the base type has no freeze node, it is a type in Standard, and
       --  always acts as its own first subtype, except where it is one of the
       --  predefined integer types. If the type is formal, it is also a first