added several syscalls for nacl mounts

sysdeps/nacl/irt_syscalls.h

 #ifndef _IRT_SYSCALLS_H
 #define _IRT_SYSCALLS_H
 
 #include <sys/types.h>
 #include <stddef.h>
 #include <fcntl.h>
 #include <time.h>
 
 #include <nacl_stat.h>
 
 struct dirent;
 struct nacl_abi_stat;
 struct timeval;
 struct timespec;
 
 extern size_t (*__nacl_irt_query)(const char *interface_ident,
                                   void *table, size_t tablesize);
 
 extern void (*__nacl_irt_exit) (int status);
 extern int (*__nacl_irt_gettod) (struct timeval *tv);
 extern int (*__nacl_irt_clock) (clock_t *ticks);
 extern int (*__nacl_irt_nanosleep) (const struct timespec *req,
                                     struct timespec *rem);
 extern int (*__nacl_irt_sched_yield) (void);
 extern int (*__nacl_irt_sysconf) (int name, int *value);
 
+extern int (*__nacl_irt_mkdir) (const char* pathname, mode_t mode);
+extern int (*__nacl_irt_rmdir) (const char* pathname);
+extern int (*__nacl_irt_chdir) (const char* pathname);
+extern char* (*__nacl_irt_getcwd) (char* buf, size_t size);
+
 extern int (*__nacl_irt_open) (const char *pathname, int oflag, mode_t cmode,
                                int *newfd);
 extern int (*__nacl_irt_close) (int fd);
 extern int (*__nacl_irt_read) (int fd, void *buf, size_t count, size_t *nread);
 extern int (*__nacl_irt_write) (int fd, const void *buf, size_t count,
                                 size_t *nwrote);
 extern int (*__nacl_irt_seek) (int fd, nacl_abi_off_t offset, int whence,
                                nacl_abi_off_t *new_offset);
 extern int (*__nacl_irt_dup) (int fd, int *newfd);
 extern int (*__nacl_irt_dup2) (int fd, int newfd);
@@ skipping 96 matching lines @@
 struct robust_list_head
 {
   void *list;
   long int futex_offset;
   void *list_op_pending;
 };
 #endif
 
 #endif
 #endif