Compilation of libxml2 on some distributions is problematic (at least
archlinux) for OpenWrt. This commit fixes the issue. Issue is caused
because configuration for some reason does not find gzopen from zlib.
This patch issues linker to include zlib anyway, if host system doesn't
have this issue, it is not a problem as linker should not link libs
twice anyway.

Signed-off-by: Oskari Rauta <oskari.rauta@gmail.com>

[ Slightly modified commit message ]
Signed-off-by: Michael Heimpold <mhei@heimpold.de>

Several packages may depend on host compiled packages during
the build time (such as the new LTS versions of telephony packages).

This commit adds an option to use the libxml2 to be built as
a host package. Usage would be following:

	PKG_BUILD_DEPENDS:=libxml2/host

Signed-off-by: Jiri Slachta <slachta@cesnet.cz>

fixes CVE-2014-3660, CVE-2014-0191 among other issues

Signed-off-by: Steven Barth <steven@midlink.org>

Signed-off-by: Michael Heimpold <mhei@heimpold.de>