libsigc: needs host-m4

Fixes
http://autobuild.buildroot.net/results/e0e5ec38208ac6cc163b6ca882690de177cb8c51/

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

package/libsigc/libsigc.mk

@@ -7,6 +7,7 @@
 LIBSIGC_VERSION = 2.2.11
 LIBSIGC_SOURCE = libsigc++-$(LIBSIGC_VERSION).tar.xz
 LIBSIGC_SITE = http://ftp.gnome.org/pub/GNOME/sources/libsigc++/2.2
+LIBSIGC_DEPENDENCIES = host-m4
 LIBSIGC_INSTALL_STAGING = YES
 LIBSIGC_LICENSE = LGPLv2.1+
 LIBSIGC_LICENSE_FILES = COPYING