[Ada] Crash on renaming within declare expression

[Pierre-Marie de Rodat via Gcc-patches]

This patch corrects an issue in the compiler whereby a renaming within a
declare expression may result in a crash in some systems.

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

gcc/ada/

        * exp_dbug.adb (Debug_Renaming_Declaration): Add check for
        Entity present for Ren to prevent looking at unanalyzed nodes
diff --git a/gcc/ada/exp_dbug.adb b/gcc/ada/exp_dbug.adb
--- a/gcc/ada/exp_dbug.adb
+++ b/gcc/ada/exp_dbug.adb
@@ -409,7 +409,9 @@ package body Exp_Dbug is
             when N_Expanded_Name
                | N_Identifier
             =>
-               if not Present (Renamed_Object (Entity (Ren))) then
+               if No (Entity (Ren))
+                 or else not Present (Renamed_Object (Entity (Ren)))
+               then
                   exit;
                end if;