https://github.com/arakiken/mlterm/pull/68

From 4eb1a0b237a861cee7ba0ceb4b69d54ab46f87f5 Mon Sep 17 00:00:00 2001
From: Sam James <sam@gentoo.org>
Date: Sun, 16 Apr 2023 11:38:16 +0100
Subject: [PATCH] Fix configure.ac compatibility with Clang 16

Clang 16 makes -Wimplicit-function-declaration and -Wimplicit-int errors by default.

Unfortunately, this can lead to misconfiguration or miscompilation of software as configure
tests may then return the wrong result.

For more information, see LWN.net [0] or LLVM's Discourse [1], the Gentoo wiki [2],
or the (new) c-std-porting mailing list [3].

Bug: https://bugs.gentoo.org/904353

[0] https://lwn.net/Articles/913505/
[1] https://discourse.llvm.org/t/configure-script-breakage-with-the-new-werror-implicit-function-declaration/65213
[2] https://wiki.gentoo.org/wiki/Modern_C_porting
[3] hosted at lists.linux.dev.
--- a/baselib/configure
+++ b/baselib/configure
@@ -13226,6 +13226,8 @@ See \`config.log' for more details" "$LINENO" 5; }
 else
   cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
+#define _XOPEN_SOURCE 600
+#include <stdlib.h>
 #include <fcntl.h>
 int
 main ()
@@ -13599,6 +13601,8 @@ else
 /* end confdefs.h.  */
 
 	#include <stdio.h>
+	#include <stdlib.h>
+	#include <stddef.h>
 	int main() {
 		return  calloc(8, ((1 << (sizeof(size_t) * 8 - 1)) + 1)) ? 1 : 0 ;
 	}
--- a/baselib/configure.in
+++ b/baselib/configure.in
@@ -285,7 +285,9 @@ elif test "$bl_cv_mingw" = "yes" ; then
 	bl_cv_pty=streams
 elif test "$host" = "$build" ; then
 	AC_CHECK_FUNC(posix_openpt,
-		[AC_RUN_IFELSE([AC_LANG_PROGRAM([#include <fcntl.h>],
+		[AC_RUN_IFELSE([AC_LANG_PROGRAM([#define _XOPEN_SOURCE 600
+						#include <stdlib.h>
+						#include <fcntl.h>],
 						[return posix_openpt(O_RDWR | O_NOCTTY) == -1;])],
 				[
 					AC_DEFINE(HAVE_POSIX_OPENPT,,"HAVE_POSIX_OPENPT")
@@ -435,6 +437,8 @@ if test "$host" = "$build"; then
 	AC_TRY_RUN(
 	[
 	#include <stdio.h>
+	#include <stdlib.h>
+	#include <stddef.h>
 	int main() {
 		return  calloc(8, ((1 << (sizeof(size_t) * 8 - 1)) + 1)) ? 1 : 0 ;
 	}
--- a/configure
+++ b/configure
@@ -25110,6 +25110,8 @@ See \`config.log' for more details" "$LINENO" 5; }
 else
   cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
+#define _XOPEN_SOURCE 600
+#include <stdlib.h>
 #include <fcntl.h>
 int
 main ()
@@ -25147,6 +25149,7 @@ else
   cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 #include <fcntl.h>
+#include <sys/stat.h>
 int
 main ()
 {
@@ -25475,6 +25478,8 @@ else
 /* end confdefs.h.  */
 
 	#include <stdio.h>
+	#include <stdlib.h>
+	#include <stddef.h>
 	int main() {
 		return  calloc(8, ((1 << (sizeof(size_t) * 8 - 1)) + 1)) ? 1 : 0 ;
 	}
--- a/configure.in
+++ b/configure.in
@@ -2150,7 +2150,9 @@ elif test "$bl_cv_mingw" = "yes" ; then
 	bl_cv_pty=streams
 elif test "$host" = "$build" ; then
 	AC_CHECK_FUNC(posix_openpt,
-		[AC_RUN_IFELSE([AC_LANG_PROGRAM([#include <fcntl.h>],
+		[AC_RUN_IFELSE([AC_LANG_PROGRAM([#define _XOPEN_SOURCE 600
+						#include <stdlib.h>
+						#include <fcntl.h>],
 						[return posix_openpt(O_RDWR | O_NOCTTY) == -1;])],
 				[
 					AC_DEFINE(HAVE_POSIX_OPENPT,,"HAVE_POSIX_OPENPT")
@@ -2160,7 +2162,8 @@ elif test "$host" = "$build" ; then
 		[bl_cv_pty=bsd])
 	if test "$bl_cv_pty" = "bsd" ; then
 		AC_RUN_IFELSE(
-			[AC_LANG_PROGRAM([#include <fcntl.h>],
+			[AC_LANG_PROGRAM([#include <sys/stat.h>
+					#include <fcntl.h>],
 					[return open( "/dev/ptmx", O_RDWR | O_NOCTTY, 0) == -1;])],
 			[bl_cv_pty=streams])
 	fi
@@ -2297,6 +2300,8 @@ if test "$host" = "$build"; then
 	AC_TRY_RUN(
 	[
 	#include <stdio.h>
+	#include <stdlib.h>
+	#include <stddef.h>
 	int main() {
 		return  calloc(8, ((1 << (sizeof(size_t) * 8 - 1)) + 1)) ? 1 : 0 ;
 	}