Fix incompatible pointers for modern C, hope that restrict qualifier
holds in this scenario
https://bugs.gentoo.org/919224
--- a/lib/localconverter.c
+++ b/lib/localconverter.c
@@ -599,12 +599,12 @@
 	inleft = 0;
 	outbuf = NULL;
 	outleft = 0;
-	iconv(ictx, (const char **)NULL, &inleft, &outbuf, &outleft);
+	iconv(ictx, NULL, &inleft, &outbuf, &outleft);
 
 	inleft = strlen(from);
 	inbuf = from;
 	outleft = tolen - 1;	/* reserve space for terminating NUL */
-	sz = iconv(ictx, (const char **)&inbuf, &inleft, &to, &outleft);
+	sz = iconv(ictx, (char ** restrict)&inbuf, &inleft, &to, &outleft);
 
 	if (sz == (size_t)(-1) || inleft > 0) {
 		switch (errno) {
@@ -630,7 +630,7 @@
 	 * Append a sequence of state reset.
 	 */
 	inleft = 0;
-	sz = iconv(ictx, (const char **)NULL, &inleft, &to, &outleft);
+	sz = iconv(ictx, NULL, &inleft, &to, &outleft);
 	if (sz == (size_t)(-1)) {
 		switch (errno) {
 		case EILSEQ: