https://bugs.gentoo.org/969309
https://gitlab.exherbo.org/exherbo/arbor/-/commit/a0a2deee48fa9377913aef8ddb2ee70f70b9e120
https://core.tcl-lang.org/tk/info/c07d5817bada4c9b
--- a/unix/tkUnixFont.c	
+++ b/unix/tkUnixFont.c	
@@ -2142,11 +2142,11 @@
      */
 
     nameList = ListFonts(fontPtr->display, "*", &numNames);
     for (i = 0; i < numNames; i++) {
 	fallback = strchr(nameList[i] + 1, '-') + 1;
-	strchr(fallback, '-')[0] = '\0';
+	strchr((char *)fallback, '-')[0] = '\0';
 	if (SeenName(fallback, &ds) == 0) {
 	    subFontPtr = CanUseFallback(fontPtr, fallback, ch,
 		    fixSubFontPtrPtr);
 	    if (subFontPtr != NULL) {
 		XFreeFontNames(nameList);