Make 'LogContext' a typedef visible throughout the code.

Same principle again - the more of these structures have globally
visible tags (even if the structure contents are still opaque in most
places), the fewer of them I can mistake for each other.

unix/uxplink.c

@@ -25,7 +25,7 @@
 
 #define MAX_STDIN_BACKLOG 4096
 
-static void *logctx;
+static LogContext *logctx;
 
 static struct termios orig_termios;