[LyX/master] By report autoconf 2.71 works, 2.70 is known to have compatibility issues.

[Pavel Sanda]

commit ddb8bd624af1493adea05e2e0a74d2a27f934e01
Author: Pavel Sanda <sanda at lyx.org>
Date:   Mon Feb 22 11:09:22 2021 +0100

    By report autoconf 2.71 works, 2.70 is known to have compatibility issues.
---
 autogen.sh |    4 +++-
 1 files changed, 3 insertions(+), 1 deletions(-)

diff --git a/autogen.sh b/autogen.sh
index edc6c40..0365a10 100755
--- a/autogen.sh
+++ b/autogen.sh
@@ -38,9 +38,11 @@ fi
 case $autoversion in
     *' '2.6[5-9])
 	;;
+    *' '2.71)
+	;;
     *)
 	echo "This autoconf version is not supported by LyX."
-	echo "LyX only supports autoconf 2.65-2.69."
+	echo "LyX only supports autoconf 2.65-2.69, 2.71."
 	exit 1
 	;;
 esac