Ensure syscall functions are consistently prefixed with "NaClSys"

src/untrusted/nacl/sbrk_private.c

 /*
  * Copyright (c) 2011 The Native Client Authors. All rights reserved.
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 /*
  * Non-IRT definition of sbrk for use only in private tests.
  */
 
 #include <errno.h>
 #include <unistd.h>
 
 #include "native_client/src/untrusted/nacl/syscall_bindings_trampoline.h"
 
 static void *current_break;
 
 void *sbrk(intptr_t increment) {
   void *old_break;
   void *new_break;
 
   if (0 == current_break)
-    current_break = NACL_SYSCALL(sysbrk)(0);
+    current_break = NACL_SYSCALL(brk)(0);
 
   old_break = current_break;
   new_break = old_break + increment;
 
   if (new_break != old_break) {
-    new_break = NACL_SYSCALL(sysbrk)(new_break);
+    new_break = NACL_SYSCALL(brk)(new_break);
     if (new_break == old_break) {
       errno = ENOMEM;
       return (void *) -1;
     }
     current_break = new_break;
   }
 
   return old_break;
 }