libpng: enable compilation on the host

libpng is needed on the host to build ace_of_penguins.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/libpng/libpng.mk

@@ -11,7 +11,12 @@ LIBPNG_INSTALL_STAGING = YES
 LIBPNG_CONF_OPT = --without-libpng-compat
 LIBPNG_DEPENDENCIES = host-pkg-config zlib
 
+HOST_LIBPNG_LIBTOOL_PATCH = NO
+HOST_LIBPNG_CONF_OPT = --without-libpng-compat
+HOST_LIBPNG_DEPENDENCIES = host-pkg-config host-zlib
+
 $(eval $(call AUTOTARGETS,package,libpng))
+$(eval $(call AUTOTARGETS,package,libpng,host))
 
 $(LIBPNG_HOOK_POST_INSTALL):
 	$(SED) "s,^prefix=.*,prefix=\'$(STAGING_DIR)/usr\',g" \