Remove warning

src/util/bt.c

@@ -28,6 +28,8 @@
 #include "bt.h"
 #include "bool.h"
 
+#if defined(HAS_BACKTRACE) || defined(HAS_LIBUNWIND) || defined(HAS_EXECINFO)
+
 static void bt_add_frame(struct backtrace *bt, const char *fname)
 {
     if (bt->frame_count >= BT_MAX_FRAMES)
@@ -41,6 +43,8 @@ static void bt_add_frame(struct backtrace *bt, const char *fname)
     bt->frame_count++;
 }
 
+#endif
+
 #ifdef HAS_BACKTRACE
 
 #include <backtrace.h>