From 6ad7a7486c3f1e1b907dadd132364fa9e611ccf0 Mon Sep 17 00:00:00 2001
From: Jim DeLaHunt <from+project_by_git@jdlh.com>
Date: Sat, 29 Jan 2022 01:28:13 -0800
Subject: [PATCH] Eliminate needless -Wimplicit-function-declaration errors on
 macOS

Configuration macro FC_FUNC_VSNPRINTF in m4/vsnprintf.m4 generates a
simple C program which uses exit() without #include <stdlib.h>, and 
strcmp() without #include <string.h>. These programs fail to #include
<stdlib.h>, so their use of exit() is implicitly declared. This has been
illegal C language since the late 1980's, but tolerated by compilers.
However, since 2019, macOS compilers have raised
-Wimplicit-function-declaration errors with such constructs. They have
good reasons to do so, related to support for ARM instruction sets.

Insert `#include <stdlib.h>` and `#include <string.h>` into this macro
in m4/vsnprintf.m4 .

Fixes ticket #43737, "Configure scripts give needless
-Wimplicit-function-declaration errors on macOS",
https://osdn.net/projects/freeciv/ticket/43737 for more information.
---
 m4/vsnprintf.m4 | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/m4/vsnprintf.m4 b/m4/vsnprintf.m4
index 87641f7479..282172fae5 100644
--- a/m4/vsnprintf.m4
+++ b/m4/vsnprintf.m4
@@ -14,6 +14,8 @@ AC_DEFUN([FC_FUNC_VSNPRINTF],
   [ac_cv_func_working_vsnprintf],
 [AC_RUN_IFELSE([AC_LANG_SOURCE([[#include <stdio.h>
 #include <stdarg.h>
+#include <stdlib.h>
+#include <string.h>
 
 int
 doit(char * s, ...)
-- 
2.35.0