opkg: fix configure step by adding host-pkgconf dependency

The opkg configure.ac uses the PKG_CHECK_MODULES() m4 macro, which is
provided by the .m4 files installed by host-pkgconf, so we must have
this package as a dependency.

Fixes:

  http://autobuild.buildroot.org/results/069fcab6e7dd5a1f07251ba6f52f65643a2f7594/build-end.log

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

package/opkg/opkg.mk

@@ -11,6 +11,8 @@ OPKG_SITE_METHOD = svn
 OPKG_INSTALL_STAGING = YES
 OPKG_CONF_OPT = --disable-curl --disable-gpg
 OPKG_AUTORECONF = YES
+# Uses PKG_CHECK_MODULES() in configure.ac
+OPKG_DEPENDENCIES = host-pkgconf
 
 # Ensure directory for lockfile exists
 define OPKG_CREATE_LOCKDIR