[Ada] Simplify redundant checks for non-empty lists

[Pierre-Marie de Rodat]

Simplify "Present (L) and then not Is_Empty_List (L)" into "not
Is_Empty_List (L)", since Is_Empty_List can be called on No_List
and returns True.

Code cleanup; semantics is unaffected.

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

gcc/ada/

        * sem_ch12.adb, sem_ch6.adb, sem_ch9.adb, sprint.adb: Simplify
        checks for non-empty lists.
diff --git a/gcc/ada/sem_ch12.adb b/gcc/ada/sem_ch12.adb
--- a/gcc/ada/sem_ch12.adb
+++ b/gcc/ada/sem_ch12.adb
@@ -9724,7 +9724,6 @@ package body Sem_Ch12 is
 
          if Nkind (Par_N) = N_Package_Specification
            and then Decls = Visible_Declarations (Par_N)
-           and then Present (Private_Declarations (Par_N))
            and then not Is_Empty_List (Private_Declarations (Par_N))
          then
             Decls := Private_Declarations (Par_N);


diff --git a/gcc/ada/sem_ch6.adb b/gcc/ada/sem_ch6.adb
--- a/gcc/ada/sem_ch6.adb
+++ b/gcc/ada/sem_ch6.adb
@@ -549,7 +549,6 @@ package body Sem_Ch6 is
             else
                if Nkind (Par) = N_Package_Specification
                  and then Decls = Visible_Declarations (Par)
-                 and then Present (Private_Declarations (Par))
                  and then not Is_Empty_List (Private_Declarations (Par))
                then
                   Decls := Private_Declarations (Par);


diff --git a/gcc/ada/sem_ch9.adb b/gcc/ada/sem_ch9.adb
--- a/gcc/ada/sem_ch9.adb
+++ b/gcc/ada/sem_ch9.adb
@@ -1955,9 +1955,7 @@ package body Sem_Ch9 is
       Tasking_Used := True;
       Analyze_Declarations (Visible_Declarations (N));
 
-      if Present (Private_Declarations (N))
-        and then not Is_Empty_List (Private_Declarations (N))
-      then
+      if not Is_Empty_List (Private_Declarations (N)) then
          Last_Id := Last_Entity (Prot_Typ);
          Analyze_Declarations (Private_Declarations (N));
 


diff --git a/gcc/ada/sprint.adb b/gcc/ada/sprint.adb
--- a/gcc/ada/sprint.adb
+++ b/gcc/ada/sprint.adb
@@ -1065,16 +1065,12 @@ package body Sprint is
                if Present (Expressions (Node)) then
                   Sprint_Comma_List (Expressions (Node));
 
-                  if Present (Component_Associations (Node))
-                    and then not Is_Empty_List (Component_Associations (Node))
-                  then
+                  if not Is_Empty_List (Component_Associations (Node)) then
                      Write_Str (", ");
                   end if;
                end if;
 
-               if Present (Component_Associations (Node))
-                 and then not Is_Empty_List (Component_Associations (Node))
-               then
+               if not Is_Empty_List (Component_Associations (Node)) then
                   Indent_Begin;
 
                   declare