gnu: Handle timeval.tv_usec for glibc 64-bit time_t

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.

References:
https://github.com/bminor/glibc/blob/e78caeb4ff812ae19d24d65f4d4d48508154277b/time/bits/types/struct_timeval.h

(backport <rust-lang#4433>)
(cherry picked from commit b63a652)

Author: snogge

src/unix/linux_like/linux/gnu/b32/mod.rs

@@ -15,6 +15,7 @@ pub type __fsword_t = i32;
 pub type fsblkcnt64_t = u64;
 pub type fsfilcnt64_t = u64;
 pub type __syscall_ulong_t = c_ulong;
+pub type __suseconds64_t = i64;
 
 cfg_if! {
     if #[cfg(target_arch = "riscv32")] {

src/unix/mod.rs

@@ -56,10 +56,14 @@ s! {
         pub modtime: time_t,
     }
 
-    // FIXME(time): Needs updates at least for glibc _TIME_BITS=64
     pub struct timeval {
         pub tv_sec: time_t,
+        #[cfg(not(gnu_time_bits64))]
         pub tv_usec: suseconds_t,
+        // For 64 bit time on 32 bit linux glibc, suseconds_t is still
+        // a 32 bit type.  Use __suseconds64_t instead
+        #[cfg(gnu_time_bits64)]
+        pub tv_usec: __suseconds64_t,
     }
 
     // linux x32 compatibility