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+# ===========================================================================
+# https://www.gnu.org/software/autoconf-archive/ax_check_gnu_make.html
+# ===========================================================================
+#
+# SYNOPSIS
+#
+# AX_CHECK_GNU_MAKE([run-if-true],[run-if-false])
+#
+# DESCRIPTION
+#
+# This macro searches for a GNU version of make. If a match is found:
+#
+# * The makefile variable `ifGNUmake' is set to the empty string, otherwise
+# it is set to "#". This is useful for including a special features in a
+# Makefile, which cannot be handled by other versions of make.
+# * The makefile variable `ifnGNUmake' is set to #, otherwise
+# it is set to the empty string. This is useful for including a special
+# features in a Makefile, which can be handled
+# by other versions of make or to specify else like clause.
+# * The variable `_cv_gnu_make_command` is set to the command to invoke
+# GNU make if it exists, the empty string otherwise.
+# * The variable `ax_cv_gnu_make_command` is set to the command to invoke
+# GNU make by copying `_cv_gnu_make_command`, otherwise it is unset.
+# * If GNU Make is found, its version is extracted from the output of
+# `make --version` as the last field of a record of space-separated
+# columns and saved into the variable `ax_check_gnu_make_version`.
+# * Additionally if GNU Make is found, run shell code run-if-true
+# else run shell code run-if-false.
+#
+# Here is an example of its use:
+#
+# Makefile.in might contain:
+#
+# # A failsafe way of putting a dependency rule into a makefile
+# $(DEPEND):
+# $(CC) -MM $(srcdir)/*.c > $(DEPEND)
+#
+# @ifGNUmake@ ifeq ($(DEPEND),$(wildcard $(DEPEND)))
+# @ifGNUmake@ include $(DEPEND)
+# @ifGNUmake@ else
+# fallback code
+# @ifGNUmake@ endif
+#
+# Then configure.in would normally contain:
+#
+# AX_CHECK_GNU_MAKE()
+# AC_OUTPUT(Makefile)
+#
+# Then perhaps to cause gnu make to override any other make, we could do
+# something like this (note that GNU make always looks for GNUmakefile
+# first):
+#
+# if ! test x$_cv_gnu_make_command = x ; then
+# mv Makefile GNUmakefile
+# echo .DEFAULT: > Makefile ;
+# echo \ $_cv_gnu_make_command \$@ >> Makefile;
+# fi
+#
+# Then, if any (well almost any) other make is called, and GNU make also
+# exists, then the other make wraps the GNU make.
+#
+# LICENSE
+#
+# Copyright (c) 2008 John Darrington <j.darrington@elvis.murdoch.edu.au>
+# Copyright (c) 2015 Enrico M. Crisostomo <enrico.m.crisostomo@gmail.com>
+#
+# Copying and distribution of this file, with or without modification, are
+# permitted in any medium without royalty provided the copyright notice
+# and this notice are preserved. This file is offered as-is, without any
+# warranty.
+
+#serial 11
+
+AC_DEFUN([AX_CHECK_GNU_MAKE],dnl
+ [AC_PROG_AWK
+ AC_CACHE_CHECK([for GNU make],[_cv_gnu_make_command],[dnl
+ _cv_gnu_make_command="" ;
+dnl Search all the common names for GNU make
+ for a in "$MAKE" make gmake gnumake ; do
+ if test -z "$a" ; then continue ; fi ;
+ if "$a" --version 2> /dev/null | grep GNU 2>&1 > /dev/null ; then
+ _cv_gnu_make_command=$a ;
+ AX_CHECK_GNU_MAKE_HEADLINE=$("$a" --version 2> /dev/null | grep "GNU Make")
+ ax_check_gnu_make_version=$(echo ${AX_CHECK_GNU_MAKE_HEADLINE} | ${AWK} -F " " '{ print $(NF); }')
+ break ;
+ fi
+ done ;])
+dnl If there was a GNU version, then set @ifGNUmake@ to the empty string, '#' otherwise
+ AS_VAR_IF([_cv_gnu_make_command], [""], [AS_VAR_SET([ifGNUmake], ["#"])], [AS_VAR_SET([ifGNUmake], [""])])
+ AS_VAR_IF([_cv_gnu_make_command], [""], [AS_VAR_SET([ifnGNUmake], [""])], [AS_VAR_SET([ifGNUmake], ["#"])])
+ AS_VAR_IF([_cv_gnu_make_command], [""], [AS_UNSET(ax_cv_gnu_make_command)], [AS_VAR_SET([ax_cv_gnu_make_command], [${_cv_gnu_make_command}])])
+ AS_VAR_IF([_cv_gnu_make_command], [""],[$2],[$1])
+ AC_SUBST([ifGNUmake])
+ AC_SUBST([ifnGNUmake])
+])