[Ada] Fix access to predicated parent in Itype

[Pierre-Marie de Rodat via Gcc-patches]

Getter function Predicated_Parent expects to be called on subtypes only,
which was not enforced always, possibly leading to assertion failures on
compiler built with assertions.

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

gcc/ada/

        * sem_ch13.adb (Build_Predicate_Functions): Access
        Predicated_Parent only on subtypes.
diff --git a/gcc/ada/sem_ch13.adb b/gcc/ada/sem_ch13.adb
--- a/gcc/ada/sem_ch13.adb
+++ b/gcc/ada/sem_ch13.adb
@@ -10191,6 +10191,9 @@ package body Sem_Ch13 is
         or else
           (Is_Itype (Typ)
            and then not Comes_From_Source (Typ)
+           and then Ekind (Typ) in E_Array_Subtype
+                                 | E_Record_Subtype
+                                 | E_Record_Subtype_With_Private
            and then Present (Predicated_Parent (Typ)))
       then
          return;