added several syscalls for nacl mounts

sysdeps/nacl/irt_syscalls.c

Index: sysdeps/nacl/irt_syscalls.c
diff --git a/sysdeps/nacl/irt_syscalls.c b/sysdeps/nacl/irt_syscalls.c
index 3706927dcea20d91664b38092ea9cd58e48cdb05..684fa707bc76a0ab3a2d193345c6b84d4bf06200 100644
--- a/sysdeps/nacl/irt_syscalls.c
+++ b/sysdeps/nacl/irt_syscalls.c
@@ -274,9 +274,18 @@ static size_t no_interface (const char *interface_ident,
   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);
@@ -545,6 +554,11 @@ init_irt_table (void)
 
   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,