package/libiconv: fix build with gcc 15.x

Fixes:
https://autobuild.buildroot.net/results/387/3875466a80e57dfd96911a2166e496cf7d41bb69/

Signed-off-by: Bernd Kuhls <bernd@kuhls.net>
Signed-off-by: Julien Olivain <ju.o@free.fr>

package/libiconv/0001-Fix-a-clang-warning-a-function-declaration-without-a-prototype.patch

@@ -0,0 +1,34 @@
+From: Bruno Haible <bruno@clisp.org>
+Date: Sun, 29 Jan 2023 19:07:21 +0000 (+0100)
+Subject: Fix a clang warning "a function declaration without a prototype...".
+X-Git-Tag: v1.18~57
+X-Git-Url: https://gitweb.git.savannah.gnu.org/gitweb/?p=libiconv.git;a=commitdiff_plain;h=e46dee2f581c1167137bcd045e114e96a9f00483
+
+Fix a clang warning "a function declaration without a prototype...".
+
+* lib/loop_wchar.h (mbrtowc): Don't declare. Drop portability to BeOS.
+
+Upstream: https://gitweb.git.savannah.gnu.org/gitweb/?p=libiconv.git;a=commitdiff;h=e46dee2f581c1167137bcd045e114e96a9f00483
+
+Signed-off-by: Bernd Kuhls <bernd@kuhls.net>
+---
+
+diff --git a/lib/loop_wchar.h b/lib/loop_wchar.h
+index b3edc29..9eb508e 100644
+--- a/lib/loop_wchar.h
++++ b/lib/loop_wchar.h
+@@ -1,5 +1,5 @@
+ /*
+- * Copyright (C) 2000-2002, 2005-2006, 2008-2009, 2011 Free Software Foundation, Inc.
++ * Copyright (C) 2000-2002, 2005-2006, 2008-2009, 2011, 2023 Free Software Foundation, Inc.
+  * This file is part of the GNU LIBICONV Library.
+  *
+  * The GNU LIBICONV Library is free software; you can redistribute it
+@@ -36,7 +36,6 @@
+ # include <wchar.h>
+ # define BUF_SIZE 64  /* assume MB_LEN_MAX <= 64 */
+   /* Some systems, like BeOS, have multibyte encodings but lack mbstate_t.  */
+-  extern size_t mbrtowc ();
+ # ifdef mbstate_t
+ #  define mbrtowc(pwc, s, n, ps) (mbrtowc)(pwc, s, n, 0)
+ #  define mbsinit(ps) 1