build: AC_USE_SYSTEM_EXTENSIONS in configure.ac.

This would, e.g. define _GNU_SOURCE in config.h, enabling the
reallocarray() prototype in glibc 2.26+ on Linux systems with that
version of glibc.

Fixes #241.

diff --git a/configure.ac b/configure.ac
index c6f12d6447148fc2e3ece35cebe3afe46b4f03ba..3c977a4e388e0d1644d037efc51eb52ed8f308f6 100644 (file)
--- a/configure.ac
+++ b/configure.ac
@@ -25,8 +25,10 @@
 # autoconf requirements and initialization
 
 AC_INIT([the fast lexical analyser generator],[2.6.4],[flex-help@lists.sourceforge.net],[flex])
+AC_PREREQ([2.60])
 AC_CONFIG_SRCDIR([src/scan.l])
 AC_CONFIG_AUX_DIR([build-aux])
+AC_USE_SYSTEM_EXTENSIONS
 LT_INIT
 AM_INIT_AUTOMAKE([1.15 -Wno-portability foreign std-options dist-lzip parallel-tests subdir-objects])
 AC_CONFIG_HEADER([src/config.h])