add readdir64 on linux
diff --git a/src/unix/notbsd/mod.rs b/src/unix/notbsd/mod.rs
index c7b714b..789d404 100644
--- a/src/unix/notbsd/mod.rs
+++ b/src/unix/notbsd/mod.rs
@@ -921,6 +921,7 @@
                    offset: off64_t) -> ::ssize_t;
     pub fn pwrite64(fd: ::c_int, buf: *const ::c_void, count: ::size_t,
                     offset: off64_t) -> ::ssize_t;
+    pub fn readdir64(dirp: *mut ::DIR) -> *mut ::dirent64;
     pub fn readdir64_r(dirp: *mut ::DIR, entry: *mut ::dirent64,
                        result: *mut *mut ::dirent64) -> ::c_int;
     pub fn setrlimit64(resource: ::c_int, rlim: *const rlimit64) -> ::c_int;