Syscall getdents64 is relatively new in linux/mips64, only since kernel
version 3.10. To support older kernel, syscall getdents is used for
mips64.

Change-Id: I892b05dff7d93e7ddb0d700abd6a5e6d4084ab4c
Reviewed-on: https://go-review.googlesource.com/14449Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Minux Ma <minux@golang.org>