fs/tar: support passing long options to tar

Move TAR_OPTS so that long options (or any option with an initial '-')
may be passed to tar. Since TAR_OPTS is at the front of the list, single
letter options still work.

Signed-off-by: Frank Hunleth <fhunleth@troodon-software.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

fs/tar/tar.mk

@@ -7,7 +7,7 @@
 TAR_OPTS := $(call qstrip,$(BR2_TARGET_ROOTFS_TAR_OPTIONS))
 
 define ROOTFS_TAR_CMD
-	tar -c$(TAR_OPTS)f $@ --numeric-owner -C $(TARGET_DIR) .
+	tar $(TAR_OPTS) -cf $@ --numeric-owner -C $(TARGET_DIR) .
 endef
 
 $(eval $(call ROOTFS_TARGET,tar))