build: use the gnulib version of the .m4 files when present

prevent aclocal from preferring .m4 files under m4/ over the version
provided by gnulib, by using only one directory.

I have noticed this after './configure --help' gave me two different
versions of "--enable-threads".  This was caused by aclocal that
preferred the version of lock.m4 provided by autopoint instead of
using the newer version distributed with gnulib.

Having two different directories made sense back when we checked
gnulib files into libvirt.git, but that was ages ago.
Signed-off-by: NGiuseppe Scrivano <gscrivan@redhat.com>
Signed-off-by: NEric Blake <eblake@redhat.com>

Makefile.am

@@ -24,7 +24,7 @@ SUBDIRS = . gnulib/lib include src daemon tools docs gnulib/tests \
   examples/dominfo examples/domsuspend examples/python examples/apparmor \
   examples/xml/nwfilter examples/openauth examples/systemtap
 
-ACLOCAL_AMFLAGS = -I m4 -I gnulib/m4
+ACLOCAL_AMFLAGS = -I m4
 
 XML_EXAMPLES = \
   $(patsubst $(srcdir)/%,%,$(wildcard $(addprefix $(srcdir)/examples/xml/, \

bootstrap.conf

@@ -175,11 +175,11 @@ fi
 # Tell gnulib to:
 #   require LGPLv2+
 #   apply any local diffs in gnulib/local/ dir
-#   put *.m4 files in new gnulib/m4/ dir
+#   put *.m4 files in m4/ dir
 #   put *.[ch] files in new gnulib/lib/ dir
 #   import gnulib tests in new gnulib/tests/ dir
 gnulib_name=libgnu
-m4_base=gnulib/m4
+m4_base=m4
 source_base=gnulib/lib
 tests_base=gnulib/tests
 gnulib_tool_option_extras="\
@@ -191,11 +191,6 @@ gnulib_tool_option_extras="\
 "
 local_gl_dir=gnulib/local
 
-# Convince bootstrap to use multiple m4 directories.
-: ${ACLOCAL=aclocal}
-ACLOCAL="$ACLOCAL -I m4"
-export ACLOCAL
-
 # Build prerequisites
 # Note that some of these programs are only required for 'make dist' to
 # succeed from a fresh git checkout; not all of these programs are