LibThread: Fix int to pointer conversion

Author: https://github.com/boricj
Commit: 8d95bd8418
Pull-request: https://github.com/SerenityOS/serenity/pull/6671
Reviewed-by: https://github.com/linusg

Userland/DevTools/HackStudio/Debugger/Debugger.h

@@ -43,7 +43,7 @@ public:
     void stop();
 
     // Thread entry point
-    static int start_static();
+    static intptr_t start_static();
 
     pthread_mutex_t* continue_mutex() { return &m_ui_action_mutex; }
     pthread_cond_t* continue_cond() { return &m_ui_action_cond; }