[Ada] Memory leak in concatenation with Initialize_Scalars

[Pierre-Marie de Rodat]

This patch fixes a memory leak in concatenation when pragma
Initialize_Scalars or Normalize_Scalars is used.

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

gcc/ada/

        * exp_ch4.adb (Expand_Concatenate): Call Set_No_Initialization
        on the N_Allocator node that is supposed to allocate on the
        secondary stack.
diff --git a/gcc/ada/exp_ch4.adb b/gcc/ada/exp_ch4.adb
--- a/gcc/ada/exp_ch4.adb
+++ b/gcc/ada/exp_ch4.adb
@@ -3505,8 +3505,17 @@ package body Exp_Ch4 is
             Alloc :=
               Make_Allocator (Loc,
                 Expression => New_Occurrence_Of (ConstrT, Loc));
+
+            --  Allocate on the secondary stack. This is currently done
+            --  only for type String, which normally doesn't have default
+            --  initialization, but we need to Set_No_Initialization in case
+            --  of Initialize_Scalars or Normalize_Scalars; otherwise, the
+            --  allocator will get transformed and will not use the secondary
+            --  stack.
+
             Set_Storage_Pool (Alloc, RTE (RE_SS_Pool));
             Set_Procedure_To_Call (Alloc, RTE (RE_SS_Allocate));
+            Set_No_Initialization (Alloc);
 
             Temp := Make_Temporary (Loc, 'R', Alloc);
             Insert_Action (Cnode,