https://bugs.gentoo.org/899072
https://github.com/heimdal/heimdal/issues/790
https://github.com/heimdal/heimdal/pull/1085

From 5b872a635c9c8f04f58e03c43e7953c35e1f66b7 Mon Sep 17 00:00:00 2001
From: Florian Weimer <fweimer@redhat.com>
Date: Thu, 13 Apr 2023 13:13:59 +0200
Subject: [PATCH 1/2] cf: Include <string.h> for memset in AC_HAVE_STRUCT_FIELD

Otherwise, the check relies on an implicit function declaration,
and will fail unconditionally with compilers that do not support
them.
--- a/cf/have-struct-field.m4
+++ b/cf/have-struct-field.m4
@@ -7,7 +7,8 @@ dnl AC_HAVE_STRUCT_FIELD(struct, field, headers)
 AC_DEFUN([AC_HAVE_STRUCT_FIELD], [
 define(cache_val, translit(ac_cv_type_$1_$2, [A-Z ], [a-z_]))
 AC_CACHE_CHECK([for $2 in $1], cache_val,[
-AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[$3]],
+AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[#include <string.h>
+$3]],
 	[[$1 x; memset(&x, 0, sizeof(x)); x.$2]])],
 	[cache_val=yes],
 	[cache_val=no])

From fc6d5b5c7677bb7271361c4bd60ea1bd36d944b9 Mon Sep 17 00:00:00 2001
From: Florian Weimer <fweimer@redhat.com>
Date: Thu, 13 Apr 2023 13:26:29 +0200
Subject: [PATCH 2/2] cf: Do not use headers and argument lists in
 AC_FIND_FUNC_NO_LIBS2

The callers of this macro generally do not supply this information.
Without it, the checks rely on compiler support for implicit function
declarations.  It would be possible to supply this information in
the callers.  But even then, with the existing macro interface, it
would be necessary to pass eg. null pointers where they trigger
undefined behavior.  Therefore, use the same kludge that autoconf
uses to make up prototypes, avoiding those implicit function
declarations.

The includes/arguments macro parameters are now ignored, but preserved
for interface compatibility.
--- a/cf/find-func-no-libs2.m4
+++ b/cf/find-func-no-libs2.m4
@@ -21,7 +21,7 @@ if eval "test \"\$ac_cv_func_$1\" != yes" ; then
 		*) ac_lib="-l$ac_lib" ;;
 		esac
 		LIBS="$6 $ac_lib $5 $ac_save_LIBS"
-		AC_LINK_IFELSE([AC_LANG_PROGRAM([[$3]],[[$1($4)]])],[eval "if test -n \"$ac_lib\";then ac_cv_funclib_$1=$ac_lib; else ac_cv_funclib_$1=yes; fi";break])
+		AC_LINK_IFELSE([AC_LANG_PROGRAM([[char $1 (void);]],[[$1()]])],[eval "if test -n \"$ac_lib\";then ac_cv_funclib_$1=$ac_lib; else ac_cv_funclib_$1=yes; fi";break])
 	done
 	eval "ac_cv_funclib_$1=\${ac_cv_funclib_$1-no}"
 	LIBS="$ac_save_LIBS"