Move Linux's POLLRDHUP into linux_like and fix its type.

This fixes two errors in #2247.

 - It moves the definitions of `POLLRDHUP` out of `linux_like/linux`
   and into `linux_like`, so that they're available on Android as well.

 - It changes the type from `c_int` to `c_short` to match the other
   `POLL*` flags.

This second change is a breaking change, and I'm fine reverting it and
leaving it as the old type if that's the right thing to do.

src/unix/linux_like/linux/mod.rs

@@ -3037,11 +3037,6 @@ pub const SOL_CAN_BASE: ::c_int = 100;
 pub const CAN_INV_FILTER: canid_t = 0x20000000;
 pub const CAN_RAW_FILTER_MAX: ::c_int = 512;
 
-#[cfg(not(any(target_arch = "sparc", target_arch = "sparc64")))]
-pub const POLLRDHUP: ::c_int = 0x2000;
-#[cfg(any(target_arch = "sparc", target_arch = "sparc64"))]
-pub const POLLRDHUP: ::c_int = 0x800;
-
 f! {
     pub fn NLA_ALIGN(len: ::c_int) -> ::c_int {
         return ((len) + NLA_ALIGNTO - 1) & !(NLA_ALIGNTO - 1)

src/unix/linux_like/mod.rs

@@ -1221,6 +1221,10 @@ pub const POLLHUP: ::c_short = 0x10;
 pub const POLLNVAL: ::c_short = 0x20;
 pub const POLLRDNORM: ::c_short = 0x040;
 pub const POLLRDBAND: ::c_short = 0x080;
+#[cfg(not(any(target_arch = "sparc", target_arch = "sparc64")))]
+pub const POLLRDHUP: ::c_short = 0x2000;
+#[cfg(any(target_arch = "sparc", target_arch = "sparc64"))]
+pub const POLLRDHUP: ::c_short = 0x800;
 
 pub const IPTOS_LOWDELAY: u8 = 0x10;
 pub const IPTOS_THROUGHPUT: u8 = 0x08;