hurd: Add missing struct __timeval for 64bit support

This is the same as linux_like/linux/gnu's __timeval for ut_tv for 64bit
architectures.

(backport <rust-lang#3786>)
(cherry picked from commit c8f2b3c)

src/unix/hurd/mod.rs

@@ -450,6 +450,11 @@ s! {
  pub tv_nsec: __syscall_slong_t,
  }
 
+ pub struct __timeval {
+ pub tv_sec: i32,
+ pub tv_usec: i32,
+ }
+
  pub struct __locale_data {
  pub _address: u8,
  }