From ad150a14598980095260add74474498a642ab5ba Mon Sep 17 00:00:00 2001
From: Nobuyoshi Nakada <nobu@ruby-lang.org>
Date: Sat, 22 Jan 2022 19:05:02 +0900
Subject: [PATCH] Override `AC_C_PROGRAM` on old autoconf

Autoconf 2.69 fails to detect `-Werror=old-style-definition` due
to the old style definition of `main`.
---
 tool/m4/ruby_try_cflags.m4 | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/tool/m4/ruby_try_cflags.m4 b/tool/m4/ruby_try_cflags.m4
index f2c6a3094e..228fe65245 100644
--- a/tool/m4/ruby_try_cflags.m4
+++ b/tool/m4/ruby_try_cflags.m4
@@ -1,4 +1,19 @@
 dnl -*- Autoconf -*-
+dnl
+dnl Autoconf 2.67 fails to detect `-Werror=old-style-definition` due
+dnl to the old style definition of `main`.
+m4_version_prereq([2.70], [], [
+m4_define([AC_LANG_PROGRAM(C)],
+[$1
+int
+main (void)
+{
+$2
+  ;
+  return 0;
+}])
+])dnl
+dnl
 AC_DEFUN([RUBY_TRY_CFLAGS], [
     AC_MSG_CHECKING([whether ]$1[ is accepted as CFLAGS])
     RUBY_WERROR_FLAG([