nuttx: Resolve warnings

Fix duplicate exports for nuttx.

(backport <#4773>)
(cherry picked from commit 82e3aed)

Author: tgross35

src/unix/mod.rs

@@ -40,6 +40,8 @@ cfg_if! {
 extern_ty! {
     pub enum DIR {}
 }
+
+#[cfg(not(target_os = "nuttx"))]
 pub type locale_t = *mut c_void;
 
 s! {
@@ -131,6 +133,7 @@ s! {
         __reserved: [c_long; 16],
     }
 
+    #[cfg(not(target_os = "nuttx"))]
     pub struct ipv6_mreq {
         pub ipv6mr_multiaddr: in6_addr,
         #[cfg(target_os = "android")]

src/unix/nuttx/mod.rs

@@ -236,11 +236,6 @@ s! {
         pub ipv6mr_multiaddr: in6_addr,
         pub ipv6mr_interface: u32,
     }
-
-    pub struct timeval {
-        pub tv_sec: time_t,
-        pub tv_usec: suseconds_t,
-    }
 }
 
 // Reserved two pointer size for reserved area for some structures.
@@ -528,7 +523,6 @@ pub const SIGQUIT: c_int = 3;
 pub const SIGILL: c_int = 4;
 pub const SIGTRAP: c_int = 5;
 pub const SIGABRT: c_int = 6;
-pub const SIGIOT: c_int = 6;
 pub const SIGBUS: c_int = 7;
 pub const SIGFPE: c_int = 8;
 pub const SIGKILL: c_int = 9;