[Ada] Initialize variable to Empty

[Pierre-Marie de Rodat via Gcc-patches]

CodePeer was warning about this variable being potentially used without
being initialized.

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

gcc/ada/

        * sem_ch8.adb (Analyze_Subprogram_Renaming): Set New_S to Empty.
diff --git a/gcc/ada/sem_ch8.adb b/gcc/ada/sem_ch8.adb
--- a/gcc/ada/sem_ch8.adb
+++ b/gcc/ada/sem_ch8.adb
@@ -3099,7 +3099,7 @@ package body Sem_Ch8 is
       --  related formal type is class-wide.
 
       Inst_Node    : Node_Id   := Empty;
-      New_S        : Entity_Id;
+      New_S        : Entity_Id := Empty;
       Wrapped_Prim : Entity_Id := Empty;
 
    --  Start of processing for Analyze_Subprogram_Renaming