[Ada] Crash freezing declaration that will raise constraint error

[Pierre-Marie de Rodat via Gcc-patches]

When the compiler is built with assertions enabled and processes the
following declarations:

   type Vector_Boolean_Array is array (1 .. 10) of Boolean;
   O2 : constant Vector_Boolean_Array := [for J in 2 => True];

The expression is rewritten by the frontend with an N_Raise_CE node,
which leads to an assertion error at the freezing point of the object
declaration.

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

gcc/ada/

        * freeze.adb (Freeze_Entity): Protect the call to
        Declaration_Node against entities of expressions replaced by the
        frontend with an N_Raise_CE node.
diff --git a/gcc/ada/freeze.adb b/gcc/ada/freeze.adb
--- a/gcc/ada/freeze.adb
+++ b/gcc/ada/freeze.adb
@@ -6582,9 +6582,13 @@ package body Freeze is
                end if;
             end if;
 
-            --  Special processing for objects created by object declaration
+            --  Special processing for objects created by object declaration;
+            --  we protect the call to Declaration_Node against entities of
+            --  expressions replaced by the frontend with an N_Raise_CE node.
 
-            if Nkind (Declaration_Node (E)) = N_Object_Declaration then
+            if Ekind (E) in E_Constant | E_Variable
+              and then Nkind (Declaration_Node (E)) = N_Object_Declaration
+            then
                Freeze_Object_Declaration (E);
             end if;