hint users about libthread_db configuration if arena not found (#2868)

* hint users about libthreaddb configuration if arena is None

* gate the hint for gdb only

pwndbg/commands/ptmalloc2.py

@@ -144,6 +144,13 @@ def print_no_arena_found_error(tid=None) -> None:
             f"No arena found for thread {message.hint(tid)} (the thread hasn't performed any allocations)."
         )
     )
+    if pwndbg.dbg.name() == pwndbg.dbg_mod.DebuggerType.GDB:
+        print(
+            message.hint(
+                "Use `set libthread-db-search-path <path>` if the path contains a compatible libthread_db.\n"
+                "Then rerun the program."
+            )
+        )
 
 
 def print_no_tcache_bins_found_error(tid: int | None = None) -> None: