Require rust >= 1.33 and drop libc_packedN conditional

[ resolve conflicts, update to latest - Trevor ]

(apply <rust-lang#4060> to `main`)
(cherry picked from commit 9dac79f)

Changes are reduced in this cherry pick compared to the original commit
because some of this was already applied to `main`.

Author: joshtriplett

src/unix/solarish/illumos.rs

@@ -46,10 +46,7 @@ s! {
 }
 
 s_no_extra_traits! {
-    #[cfg_attr(any(
-        target_arch = "x86", target_arch = "x86_64"),
-        repr(packed(4))
-    )]
+    #[cfg_attr(any(target_arch = "x86", target_arch = "x86_64"), repr(packed(4)))]
     pub struct epoll_event {
         pub events: u32,
         pub u64: u64,