The standard iconv function uses char ** even for its input
argument. With a const char ** argument, ICONV_NONTRANS is incorrectly
set to 1 if the compiler produces an error for such incompatible
pointer types.

Submitted upstream: <https://gitlab.com/muttmua/mutt/-/merge_requests/175>

diff --git a/configure.ac b/configure.ac
index 9fe461df2a5af3a8..443da363081343c5 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1322,10 +1322,10 @@ AC_CACHE_CHECK([whether iconv is non-transcribing], mutt_cv_iconv_nontrans,
 int main()
 {
   iconv_t cd;
-  const char *ib;
+  char *ib;
   char *ob;
   size_t ibl, obl;
-  const char *s = "\304\211";
+  char *s = (char *) "\304\211";
 changequote(, )dnl
   char t[3];
 changequote([, ])dnl