added several syscalls for nacl mounts

sysdeps/nacl/irt_syscalls.c

 #include <string.h>
 #include <sys/stat.h>
 #include <time.h>
 #include <nacl_stat.h>
 #include <nacl_syscalls.h>
 #define stat nacl_abi_stat
 #include <irt.h>
 #undef stat
 #include <irt_syscalls.h>
 #ifdef IS_IN_rtld
@@ skipping 256 matching lines @@
 static int nacl_irt_clock_gettime(clockid_t clk_id,
                                   struct timespec *tp) {
   return -NACL_SYSCALL (clock_gettime) (clk_id, tp);
 }
 
 static size_t no_interface (const char *interface_ident,
                             void *table, size_t tablesize) {
   return 0;
 }
 
+static int not_implemented() {
+  return (12 /* ENOSYS */);
+}
+
 size_t (*__nacl_irt_query) (const char *interface_ident,
                             void *table, size_t tablesize);
 
+int (*__nacl_irt_mkdir) (const char* pathname, mode_t mode);
+int (*__nacl_irt_rmdir) (const char* pathname);
+int (*__nacl_irt_chdir) (const char* pathname);
+int (*__nacl_irt_getcwd) (char* buf, size_t size, int* ret);
+
 void (*__nacl_irt_exit) (int status);
 int (*__nacl_irt_gettod) (struct timeval *tv);
 int (*__nacl_irt_clock) (clock_t *ticks);
 int (*__nacl_irt_nanosleep) (const struct timespec *req, struct timespec *rem);
 int (*__nacl_irt_sched_yield) (void);
 int (*__nacl_irt_sysconf) (int name, int *value);
 
 int (*__nacl_irt_open) (const char *pathname, int oflag, mode_t cmode,
                         int *newfd);
 int (*__nacl_irt_close) (int fd);
@@ skipping 248 matching lines @@
       __nacl_irt_clock_gettime = u.nacl_irt_clock.gettime;
     }
   else
     {
       __nacl_irt_clock_getres = nacl_irt_clock_getres;
       __nacl_irt_clock_gettime = nacl_irt_clock_gettime;
     }
 
   if (!__nacl_irt_query)
     __nacl_irt_query = no_interface;
+
+  __nacl_irt_mkdir = not_implemented;
+  __nacl_irt_chdir = not_implemented;
+  __nacl_irt_rmdir = not_implemented;
+  __nacl_irt_getcwd = not_implemented;
 }
 
 size_t nacl_interface_query(const char *interface_ident,
                             void *table, size_t tablesize) {
   return (*__nacl_irt_query)(interface_ident, table, tablesize);
 }