linux: Handle timeval.tv_usec for linux __USE_TIME_BITS64

For 64 bit time on 32 bit linux glibc timeval.tv_usec is actually
__suseconds64_t (64 bits) while suseconds_t is still 32 bits.

Author: snogge

src/unix/mod.rs

@@ -68,7 +68,12 @@ s! {
 
     pub struct timeval {
         pub tv_sec: time_t,
+        #[cfg(not(linux_time_bits64))]
         pub tv_usec: suseconds_t,
+        // For 64 bit time on 32 bit linux glibc, suseconds_t is still
+        // a 32 bit type.  Using suseconds_t here will break the tests, use i64 instead
+        #[cfg(linux_time_bits64)]
+        pub tv_usec: i64,
     }
 
     // linux x32 compatibility