gnu: Update struct aiocb for gnu_file_offset_bits64

(backport <rust-lang#4345>)
(cherry picked from commit 7ba56f2)

Author: snogge

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

@@ -32,7 +32,11 @@ s! {
         __error_code: c_int,
         __return_value: ssize_t,
         pub aio_offset: off_t,
-        #[cfg(all(not(target_arch = "x86_64"), target_pointer_width = "32"))]
+        #[cfg(all(
+            not(gnu_file_offset_bits64),
+            not(target_arch = "x86_64"),
+            target_pointer_width = "32"
+        ))]
         __unused1: [c_char; 4],
         __glibc_reserved: [c_char; 32],
     }