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# ===========================================================================
# http://www.gnu.org/software/autoconf-archive/ax_check_gnu_make.html
# ===========================================================================
#
# SYNOPSIS
#
# AX_CHECK_GNU_MAKE()
#
# 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 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`.
#
# 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 $(DEPEND)
# @ifGNUmake@ endif
#
# Then configure.in would normally contain:
#
# AX_CHECK_GNU_MAKE()
# AC_OUTPUT(Makefile)
#
# Then perhaps to cause gnu make to override any other make, we could do
# something like this (note that GNU make always looks for GNUmakefile
# first):
#
# if ! test x$_cv_gnu_make_command = x ; then
# mv Makefile GNUmakefile
# echo .DEFAULT: > Makefile ;
# echo \ $_cv_gnu_make_command \$@ >> Makefile;
# fi
#
# Then, if any (well almost any) other make is called, and GNU make also
# exists, then the other make wraps the GNU make.
#
# LICENSE
#
# Copyright (c) 2008 John Darrington <j.darrington@elvis.murdoch.edu.au>
# Copyright (c) 2015 Enrico M. Crisostomo <enrico.m.crisostomo@gmail.com>
#
# Copying and distribution of this file, with or without modification, are
# permitted in any medium without royalty provided the copyright notice
# and this notice are preserved. This file is offered as-is, without any
# warranty.
#serial 8
AC_DEFUN([AX_CHECK_GNU_MAKE],dnl
[AC_PROG_AWK
AC_CACHE_CHECK([for GNU make],[_cv_gnu_make_command],[dnl
_cv_gnu_make_command="" ;
dnl Search all the common names for GNU make
for a in "$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 $(NF); }')
break ;
fi
done ;])
dnl If there was a GNU version, then set @ifGNUmake@ to the empty string, '#' otherwise
AS_VAR_IF([_cv_gnu_make_command], [""], [AS_VAR_SET([ifGNUmake], ["#"])], [AS_VAR_SET([ifGNUmake], [""])])
AS_VAR_IF([_cv_gnu_make_command], [""], [AS_UNSET(ax_cv_gnu_make_command)], [AS_VAR_SET([ax_cv_gnu_make_command], [${_cv_gnu_make_command}])])
AC_SUBST([ifGNUmake])
])
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