Fix up siginfo_t for mips targets

Author: bossmc

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

@@ -146,10 +146,15 @@ s! {
         pub sa_restorer: ::Option<extern fn()>,
     }
 
+    // `mips*` targets swap the `s_errno` and `s_code` fields otherwise this struct is
+    // target-agnostic (see https://www.openwall.com/lists/musl/2016/01/27/1/2)
     pub struct siginfo_t {
         pub si_signo: ::c_int,
+        #[cfg(not(target_arch = "mips"))]
         pub si_errno: ::c_int,
         pub si_code: ::c_int,
+        #[cfg(target_arch = "mips")]
+        pub si_errno: ::c_int,
         #[doc(hidden)]
         #[deprecated(
             since="0.2.54",