[Ada] Fix clearly unintentional dead analysis of attribute Code_Address

[Pierre-Marie de Rodat via Gcc-patches]

A new warning about unreachable code that follows calls to procedures
with No_Return would flag a clearly unintentional dead call to
Set_Address_Taken in analysis of Code_Address attribute.

This patch resurrects the dead code, which is worth fixing regardless of
the new warning.

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

gcc/ada/

        * sem_attr.adb (Analyze_Attribute): Move call to
        Set_Address_Taken so that it is executed when the prefix
        attribute is legal.
diff --git a/gcc/ada/sem_attr.adb b/gcc/ada/sem_attr.adb
--- a/gcc/ada/sem_attr.adb
+++ b/gcc/ada/sem_attr.adb
@@ -3746,11 +3746,11 @@ package body Sem_Attr is
                     Ekind (Entity (P)) /= E_Procedure)
          then
             Error_Attr ("invalid prefix for % attribute", P);
-            Set_Address_Taken (Entity (P));
 
          --  Issue an error if the prefix denotes an eliminated subprogram
 
          else
+            Set_Address_Taken (Entity (P));
             Check_For_Eliminated_Subprogram (P, Entity (P));
          end if;