libpng: convert old-style hook to new-style hook

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

package/libpng/libpng.mk

@@ -14,14 +14,15 @@ LIBPNG_DEPENDENCIES = host-pkg-config zlib
 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):
+define LIBPNG_STAGING_LIBPNG12_CONFIG_FIXUP
 	$(SED) "s,^prefix=.*,prefix=\'$(STAGING_DIR)/usr\',g" \
 		-e "s,^exec_prefix=.*,exec_prefix=\'$(STAGING_DIR)/usr\',g" \
 		-e "s,^includedir=.*,includedir=\'$(STAGING_DIR)/usr/include/libpng12\',g" \
 		-e "s,^libdir=.*,libdir=\'$(STAGING_DIR)/usr/lib\',g" \
 		$(STAGING_DIR)/usr/bin/libpng12-config
-	touch $@
+endef
 
+LIBPNG_POST_INSTALL_STAGING_HOOKS += LIBPNG_STAGING_LIBPNG12_CONFIG_FIXUP
+
+$(eval $(call AUTOTARGETS,package,libpng))
+$(eval $(call AUTOTARGETS,package,libpng,host))