Build fixes for fnl/musl

runtime/vm/virtual_memory_linux.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/globals.h"
 #if defined(TARGET_OS_LINUX)
 
 #include "vm/virtual_memory.h"
 
 #include <sys/mman.h>  // NOLINT
-#include <sys/unistd.h>  // NOLINT
 #include <unistd.h>  // NOLINT
 
 #include "platform/assert.h"
 #include "platform/utils.h"
 
 namespace dart {
 
 // standard MAP_FAILED causes "error: use of old-style cast" as it
 // defines MAP_FAILED as ((void *) -1)
 #undef MAP_FAILED
@@ skipping 79 matching lines @@
   }
   return (mprotect(reinterpret_cast<void*>(page_address),
                    end_address - page_address,
                    prot) == 0);
 }
 
 
 }  // namespace dart
 
 #endif  // defined(TARGET_OS_LINUX)