https://github.com/proftpd/proftpd/pull/1754

From 020192499202f268e6d96339597921aec01ec737 Mon Sep 17 00:00:00 2001
From: Florian Weimer <fweimer@redhat.com>
Date: Fri, 8 Dec 2023 19:58:51 +0100
Subject: [PATCH] configure: Use char ** for the iconv input argument

The standard iconv function uses char ** even for the input buffer.
Using the incompatible const char ** type causes the check to fail if
the compiler treats such type errors as errors, instead of merely
warning about it.
--- a/configure
+++ b/configure
@@ -21475,7 +21475,7 @@ main ()
 {
 
     size_t res, in_len = 0, out_len = 0;
-    const char *in = NULL;
+    char *in = NULL;
     char *out = NULL;
     res = iconv((iconv_t)-1, &in, &in_len, &out, &out_len);
 
--- a/configure.in
+++ b/configure.in
@@ -2100,7 +2100,7 @@ AC_TRY_LINK(
   ],
   [ 
     size_t res, in_len = 0, out_len = 0;
-    const char *in = NULL;
+    char *in = NULL;
     char *out = NULL;
     res = iconv((iconv_t)-1, &in, &in_len, &out, &out_len);
   ],