gdk-pixbuf: copy loaders.cache later on

Trying to copy loaders.cache from host-gdk-pixbuf to the gdk-pixbuf
build directory in the post-patch hook is too early when using TLP (it
breaks horribly) since host-gdk-pixbuf isn't built yet during the
massive unpack/patch cycle.
Switch it to the pre-build hook instead which ensures that gdk-pixbuf
dependencies were already built.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/gdk-pixbuf/gdk-pixbuf.mk

@@ -80,7 +80,7 @@ define GDK_PIXBUF_COPY_LOADERS_CACHE
 	cp -f $(HOST_DIR)/usr/lib/gdk-pixbuf-2.0/2.10.0/loaders.cache \
 		$(@D)/gdk-pixbuf
 endef
-GDK_PIXBUF_POST_PATCH_HOOKS += GDK_PIXBUF_COPY_LOADERS_CACHE
+GDK_PIXBUF_PRE_BUILD_HOOKS += GDK_PIXBUF_COPY_LOADERS_CACHE
 
 $(eval $(autotools-package))
 $(eval $(host-autotools-package))