[Ada] Switch from __sync to __atomic builtins for atomic counters

[Pierre-Marie de Rodat via Gcc-patches]

Unit System.Atomic_Counters was using deprecated __sync GCC builtins.
Now it uses __atomic builtins, which are recommended for new code.

Tested on x86_64-pc-linux-gnu, committed on trunk

gcc/ada/

        * libgnat/s-atocou__builtin.adb (Decrement, Increment): Switch
        from __sync to __atomic builtins; use 'Address to be consistent
        with System.Atomic_Primitives.
diff --git a/gcc/ada/libgnat/s-atocou__builtin.adb b/gcc/ada/libgnat/s-atocou__builtin.adb
--- a/gcc/ada/libgnat/s-atocou__builtin.adb
+++ b/gcc/ada/libgnat/s-atocou__builtin.adb
@@ -29,21 +29,27 @@
 --                                                                          --
 ------------------------------------------------------------------------------
 
---  This package implements Atomic_Counter and Atomic_Unsigned operations
---  for platforms where GCC supports __sync_add_and_fetch_4 and
---  __sync_sub_and_fetch_4 builtins.
+--  This package implements Atomic_Counter and Atomic_Unsigned operations for
+--  platforms where GCC supports __atomic_add_fetch and __atomic_sub_fetch
+--  builtins.
+
+with System.Atomic_Primitives; use System.Atomic_Primitives;
 
 package body System.Atomic_Counters is
 
-   procedure Sync_Add_And_Fetch
-     (Ptr   : access Atomic_Unsigned;
-      Value : Atomic_Unsigned);
-   pragma Import (Intrinsic, Sync_Add_And_Fetch, "__sync_add_and_fetch_4");
+   function Atomic_Add_Fetch
+     (Ptr   : System.Address;
+      Val   : Atomic_Unsigned;
+      Model : Mem_Model := Seq_Cst)
+     return Atomic_Unsigned;
+   pragma Import (Intrinsic, Atomic_Add_Fetch, "__atomic_add_fetch");
 
-   function Sync_Sub_And_Fetch
-     (Ptr   : access Atomic_Unsigned;
-      Value : Atomic_Unsigned) return Atomic_Unsigned;
-   pragma Import (Intrinsic, Sync_Sub_And_Fetch, "__sync_sub_and_fetch_4");
+   function Atomic_Sub_Fetch
+     (Ptr   : System.Address;
+      Val   : Atomic_Unsigned;
+      Model : Mem_Model := Seq_Cst)
+     return Atomic_Unsigned;
+   pragma Import (Intrinsic, Atomic_Sub_Fetch, "__atomic_sub_fetch");
 
    ---------------
    -- Decrement --
@@ -51,19 +57,19 @@ package body System.Atomic_Counters is
 
    procedure Decrement (Item : aliased in out Atomic_Unsigned) is
    begin
-      if Sync_Sub_And_Fetch (Item'Unchecked_Access, 1) = 0 then
+      if Atomic_Sub_Fetch (Item'Address, 1) = 0 then
          null;
       end if;
    end Decrement;
 
    function Decrement (Item : aliased in out Atomic_Unsigned) return Boolean is
    begin
-      return Sync_Sub_And_Fetch (Item'Unchecked_Access, 1) = 0;
+      return Atomic_Sub_Fetch (Item'Address, 1) = 0;
    end Decrement;
 
    function Decrement (Item : in out Atomic_Counter) return Boolean is
    begin
-      return Sync_Sub_And_Fetch (Item.Value'Unchecked_Access, 1) = 0;
+      return Atomic_Sub_Fetch (Item.Value'Address, 1) = 0;
    end Decrement;
 
    ---------------
@@ -72,12 +78,16 @@ package body System.Atomic_Counters is
 
    procedure Increment (Item : aliased in out Atomic_Unsigned) is
    begin
-      Sync_Add_And_Fetch (Item'Unchecked_Access, 1);
+      if Atomic_Add_Fetch (Item'Address, 1) = 0 then
+         null;
+      end if;
    end Increment;
 
    procedure Increment (Item : in out Atomic_Counter) is
    begin
-      Sync_Add_And_Fetch (Item.Value'Unchecked_Access, 1);
+      if Atomic_Add_Fetch (Item.Value'Address, 1) = 0 then
+         null;
+      end if;
    end Increment;
 
    ----------------