This is duplicated code from Tk.
It causes errors during build since XLowerWindow is not only a function but also "defined" in tkIntXlibDecls.h.

See
https://github.com/tcltk/tk/blob/71dcaddc69769cbd3e2c4b5edb5810f974579527/generic/tkIntXlibDecls.h#L396
and
https://github.com/tcltk/tk/blob/71dcaddc69769cbd3e2c4b5edb5810f974579527/generic/tkIntXlibDecls.h#L1487

--- a/unix/tixUnixWm.c	2005-03-25 13:15:53.000000000 -0700
+++ b/unix/tixUnixWm.c	2021-03-20 07:31:52.000000000 -0700
@@ -24,38 +24,3 @@
 {
     return TCL_OK;
 }
-
-#ifdef MAC_OSX_TK
-#include "tkInt.h"
-/*
- *----------------------------------------------------------------------
- *
- * XLowerWindow --
- *
- *	Change the stacking order of a window.
- *
- * Results:
- *	None.
- *
- * Side effects:
- *	Changes the stacking order of the specified window.
- *
- *----------------------------------------------------------------------
- */
-
-int 
-XLowerWindow(
-    Display* display,		/* Display. */
-    Window window)		/* Window. */
-{
-    TkWindow *winPtr = *((TkWindow **) window);
-    
-    display->request++;
-    if (Tk_IsTopLevel(winPtr) && !Tk_IsEmbedded(winPtr)) {
-	TkWmRestackToplevel(winPtr, Below, NULL);
-    } else {
-    	/* TODO: this should generate damage */
-    }
-    return 0;
-}
-#endif