build: require GNU make in order to run the maintainer checks

This is not a real regression in portability, since most maintainer
check rules already assumed GNU grep, and were anyway only meant to
run on the developers' systems (where we can safely assume the
presence of GNU make).

This change will allow us to take advantage, in future changes, of
more GNU make features, thus simplifying or optimizing some of our
maintainer rules.

* GNUmakefile: New, including 'Makefile' and 'syntax-checks.mk'.
* configure.ac (AC_CONFIG_LINKS): Link it in the builddir.
* Makefile.am (EXTRA_DIST): Distribute 'GNUmakefile' and
'syntax-checks.mk'.
Move all syntax-check rules and auxiliary variables into ...
* syntax-checks.mk: ... this new file, with some adjustments.

1 files changed, 19 insertions, 0 deletions

diff --git a/GNUmakefile b/GNUmakefile
new file mode 100644
index 000000000..134e74323
--- /dev/null
+++ b/GNUmakefile
@@ -0,0 +1,19 @@
+# Maintainer makefile for Automake.  Requires GNU make.
+
+# Copyright (C) 2012 Free Software Foundation, Inc.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2, or (at your option)
+# any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+include ./Makefile
+include $(srcdir)/syntax-checks.mk