Fix build on emscripten

Author: asomers

libc-test/build.rs

@@ -2844,6 +2844,8 @@ fn test_emscripten(target: &str) {
     });
 
     cfg.skip_field(move |struct_, field| {
+        // _sigev_un is an anonymous union
+        (struct_ == "sigevent" && field == "_sigev_un") ||
         // this is actually a union on linux, so we can't represent it well and
         // just insert some padding.
         // FIXME: is this necessary?

src/unix/linux_like/emscripten/mod.rs

@@ -171,23 +171,6 @@ s! {
         pub sem_flg: ::c_short,
     }
 
-    pub struct aiocb {
-        pub aio_fildes: ::c_int,
-        pub aio_lio_opcode: ::c_int,
-        pub aio_reqprio: ::c_int,
-        pub aio_buf: *mut ::c_void,
-        pub aio_nbytes: ::size_t,
-        pub aio_sigevent: ::sigevent,
-        __td: *mut ::c_void,
-        __lock: [::c_int; 2],
-        __err: ::c_int,
-        __ret: ::ssize_t,
-        pub aio_offset: off_t,
-        __next: *mut ::c_void,
-        __prev: *mut ::c_void,
-        __dummy4: [::c_char; 24],
-    }
-
     pub struct sigaction {
         pub sa_sigaction: ::sighandler_t,
         pub sa_mask: ::sigset_t,
@@ -351,6 +334,24 @@ s! {
 }
 
 s_no_extra_traits! {
+    #[cfg_attr(feature = "extra_traits", derive(Debug))]
+    pub struct aiocb {
+        pub aio_fildes: ::c_int,
+        pub aio_lio_opcode: ::c_int,
+        pub aio_reqprio: ::c_int,
+        pub aio_buf: *mut ::c_void,
+        pub aio_nbytes: ::size_t,
+        pub aio_sigevent: ::sigevent,
+        __td: *mut ::c_void,
+        __lock: [::c_int; 2],
+        __err: ::c_int,
+        __ret: ::ssize_t,
+        pub aio_offset: off_t,
+        __next: *mut ::c_void,
+        __prev: *mut ::c_void,
+        __dummy4: [::c_char; 24],
+    }
+
     pub struct dirent {
         pub d_ino: ::ino_t,
         pub d_off: ::off_t,