libpng: 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/libpng/libpng.mk

@@ -12,6 +12,7 @@ LIBPNG_LICENSE = libpng license
 LIBPNG_LICENSE_FILES = LICENSE
 LIBPNG_INSTALL_STAGING = YES
 LIBPNG_DEPENDENCIES = host-pkgconf zlib
+HOST_LIBPNG_DEPENDENCIES = host-pkgconf host-zlib
 LIBPNG_CONFIG_SCRIPTS = libpng$(LIBPNG_SERIES)-config libpng-config
 LIBPNG_CONF_OPTS = $(if $(BR2_ARM_CPU_HAS_NEON),--enable-arm-neon=yes,--enable-arm-neon=no)