libtool: add explicit dependencies for host variant

Signed-off-by: Julien Floret <julien.floret@6wind.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/libtool/libtool.mk

@@ -10,6 +10,7 @@ LIBTOOL_SITE = $(BR2_GNU_MIRROR)/libtool
 LIBTOOL_INSTALL_STAGING = YES
 LIBTOOL_CONF_ENV = HELP2MAN=true
 LIBTOOL_DEPENDENCIES = host-m4
+HOST_LIBTOOL_DEPENDENCIES = host-m4
 LIBTOOL_LICENSE = GPLv2+
 LIBTOOL_LICENSE_FILES = COPYING