infra: fix "<pkg>-rebuild" when using rsync source feature

Because the configure stamp file depends on the rsync stamp file,
removing it by the "<pkg>-clean-for-rebuild" rule trigger the configure
step. To avoid triggering the configure step use an order-only dependency.

Signed-off-by: Fabio Porcedda <fabio.porcedda@gmail.com>
Reported-by: Cédric Marie <cedric.marie@openmailbox.org>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/pkg-generic.mk

@@ -545,7 +545,10 @@ else
 #  source, by rsyncing
 #  depends
 #  configure
-$$($(2)_TARGET_CONFIGURE):	$$($(2)_TARGET_RSYNC)
+
+# Use an order-only dependency so the "<pkg>-clean-for-rebuild" rule
+# can remove the stamp file without triggering the configure step.
+$$($(2)_TARGET_CONFIGURE): | $$($(2)_TARGET_RSYNC)
 
 $(1)-depends:		$$($(2)_FINAL_DEPENDENCIES)