Use (void) in prototypes instead of ().

Also, removed `__inline` from an extern function (why was it there?).
Also, moved one extern declaration to a header file. There are lots of
these that need to be moved, but one thing at a time.

src/prompt.h

@@ -40,6 +40,8 @@ typedef struct {
     struct friend_request request[MAX_FRIEND_REQUESTS];
 } FriendRequests;
 
+extern FriendRequests FrndRequests;
+
 ToxWindow new_prompt(void);
 
 void prep_prompt_win(void);