[Ada] Simplify type conversions in source pointer arithmetic

[Pierre-Marie de Rodat via Gcc-patches]

Code cleanup; semantics is unaffacted.

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

gcc/ada/

        * sem_res.adb (Resolve_String_Literal): Simplify pointer
        arithmetic.
diff --git a/gcc/ada/sem_res.adb b/gcc/ada/sem_res.adb
--- a/gcc/ada/sem_res.adb
+++ b/gcc/ada/sem_res.adb
@@ -11737,7 +11737,7 @@ package body Sem_Res is
                         Apply_Compile_Time_Constraint_Error
                           (N, "character out of range??",
                            CE_Range_Check_Failed,
-                           Loc => Source_Ptr (Int (Loc) + J));
+                           Loc => Loc + Source_Ptr (J));
                      end if;
                   end loop;