fake POSIX exit codes consequently on windows

We faked these before when the invoked command already had shut down, now
we also do the right thing when we explicitly close it.

src/io/syncpipe.c

@@ -35,6 +35,7 @@ static MVMint64 do_close(MVMThreadContext *tc, MVMIOSyncPipeData *data) {
         if (!uv_is_closing((uv_handle_t*)data->process))
             uv_process_close(tc->loop, data->process);
         GetExitCodeProcess(data->process->process_handle, &status);
+        status = status << 8;
 #else
         waitpid(data->process->pid, &status, 0);
 #endif
@@ -52,7 +53,7 @@ static MVMint64 do_close(MVMThreadContext *tc, MVMIOSyncPipeData *data) {
         MVM_string_decodestream_destory(tc, data->ss.ds);
         data->ss.ds = NULL;
     }
-    return status;
+    return (MVMint64)status;
 }
 static MVMint64 closefh(MVMThreadContext *tc, MVMOSHandle *h) {
     MVMIOSyncPipeData *data = (MVMIOSyncPipeData *)h->body.data;