From 0c053f97337fa4ead77acefb577e8e86f8ef388d Mon Sep 17 00:00:00 2001
From: Lasse Collin <lasse.collin@tukaani.org>
Date: Tue, 21 Mar 2023 14:07:51 +0200
Subject: [PATCH] Build: Add a comment that AC_PROG_CC_C99 is needed for
 Autoconf 2.69.

It's obsolete in Autoconf >= 2.70 and just an alias for AC_PROG_CC
but Autoconf 2.69 requires AC_PROG_CC_C99 to get a C99 compiler.
---
 configure.ac | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/configure.ac b/configure.ac
index a1f76c4d..9ab921e1 100644
--- a/configure.ac
+++ b/configure.ac
@@ -602,6 +602,9 @@ echo "Initializing Automake:"
 AM_INIT_AUTOMAKE([1.12 foreign tar-v7 filename-length-max=99 -Wno-unsupported])
 AC_PROG_LN_S
 
+dnl # Autoconf >= 2.70 warns that AC_PROG_CC_C99 is obsolete. However,
+dnl # we have to keep using AC_PROG_CC_C99 instead of AC_PROG_CC
+dnl # as long as we try to be compatible with Autoconf 2.69.
 AC_PROG_CC_C99
 if test x$ac_cv_prog_cc_c99 = xno ; then
 	AC_MSG_ERROR([No C99 compiler was found.])