Move thread_pool.h into utils so it can be shared by more than one example.

native_client_sdk/src/libraries/nacl_io/kernel_wrap_real.h

 /* Copyright (c) 2012 The Chromium Authors. All rights reserved.
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 #ifndef LIBRARIES_NACL_IO_KERNEL_WRAP_REAL_H_
 #define LIBRARIES_NACL_IO_KERNEL_WRAP_REAL_H_
 
 #include "nacl_io/ostypes.h"
-#include "utils/macros.h"
+#include "sdk_util/macros.h"
 
 EXTERN_C_BEGIN
 
 int _real_close(int fd);
 int _real_fstat(int fd, struct stat *buf);
 int _real_getdents(int fd, void* nacl_buf, size_t nacl_count, size_t *nread);
 int _real_lseek(int fd, off_t offset, int whence, off_t* new_offset);
 int _real_mkdir(const char* pathname, mode_t mode);
 int _real_mmap(void** addr, size_t length, int prot, int flags, int fd,
                off_t offset);
 int _real_munmap(void* addr, size_t length);
 int _real_open(const char* pathname, int oflag, mode_t cmode, int* newfd);
 int _real_open_resource(const char* file, int* fd);
 int _real_read(int fd, void *buf, size_t count, size_t *nread);
 int _real_rmdir(const char* pathname);
 int _real_write(int fd, const void *buf, size_t count, size_t *nwrote);
 
 EXTERN_C_END
 
 #endif  // LIBRARIES_NACL_IO_KERNEL_WRAP_REAL_H_