linux, fuchsia: Mark mq_attr padding area as such

As per commit c100954 the hard-coded partial equality implementations
have been dropped in favor for auto-generated ones, but they did not
work for mq_attr, since the padding area was not typed correctly.

Fix this, using the Padding type.

Author: 3v1n0

src/fuchsia/mod.rs

@@ -941,7 +941,7 @@ s! {
         #[cfg(all(target_arch = "x86_64", target_pointer_width = "32"))]
         pub mq_curmsgs: i64,
         #[cfg(all(target_arch = "x86_64", target_pointer_width = "32"))]
-        pad: [i64; 4],
+        pad: Padding<[i64; 4]>,
 
         #[cfg(not(all(target_arch = "x86_64", target_pointer_width = "32")))]
         pub mq_flags: c_long,
@@ -952,7 +952,7 @@ s! {
         #[cfg(not(all(target_arch = "x86_64", target_pointer_width = "32")))]
         pub mq_curmsgs: c_long,
         #[cfg(not(all(target_arch = "x86_64", target_pointer_width = "32")))]
-        pad: [c_long; 4],
+        pad: Padding<[c_long; 4]>,
     }
 
     pub struct sockaddr_nl {

src/unix/linux_like/emscripten/mod.rs

@@ -365,7 +365,7 @@ s! {
         pub mq_maxmsg: c_long,
         pub mq_msgsize: c_long,
         pub mq_curmsgs: c_long,
-        pad: [c_long; 4],
+        pad: Padding<[c_long; 4]>,
     }
 
     #[cfg_attr(target_pointer_width = "32", repr(align(4)))]

src/unix/linux_like/linux/mod.rs

@@ -1424,7 +1424,7 @@ s! {
         #[cfg(all(target_arch = "x86_64", target_pointer_width = "32"))]
         pub mq_curmsgs: i64,
         #[cfg(all(target_arch = "x86_64", target_pointer_width = "32"))]
-        pad: [i64; 4],
+        pad: Padding<[i64; 4]>,
 
         #[cfg(not(all(target_arch = "x86_64", target_pointer_width = "32")))]
         pub mq_flags: c_long,
@@ -1435,7 +1435,7 @@ s! {
         #[cfg(not(all(target_arch = "x86_64", target_pointer_width = "32")))]
         pub mq_curmsgs: c_long,
         #[cfg(not(all(target_arch = "x86_64", target_pointer_width = "32")))]
-        pad: [c_long; 4],
+        pad: Padding<[c_long; 4]>,
     }
 
     pub struct hwtstamp_config {