PR go/89447
    syscall, internal/syscall: adjust use of largefile functions
    
    Consistently call __go_openat for openat.  Use fstatat64, creat64,
    sendfile64, and getdents64 where needed.
    
    Based on patch by Rainer Orth.
    
    Fixes https://gcc.gnu.org/PR89447
    
    Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/166420

From-SVN: r269521