fs/common: build host-xz when xz compression is used

When a filesystem image is xz-compressed, the XZ variable is used to refer
to the xz compression tool, but it is not necessarily available. Add a
proper dependency to fix that.

Signed-off-by: Thomas De Schampheleire <thomas.de.schampheleire@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

fs/common.mk

@@ -62,6 +62,7 @@ ROOTFS_$(2)_COMPRESS_EXT = .lzo
 ROOTFS_$(2)_COMPRESS_CMD = $$(LZOP) -9 -c
 endif
 ifeq ($$(BR2_TARGET_ROOTFS_$(2)_XZ),y)
+ROOTFS_$(2)_DEPENDENCIES += host-xz
 ROOTFS_$(2)_COMPRESS_EXT = .xz
 ROOTFS_$(2)_COMPRESS_CMD = xz -9 -C crc32 -c
 endif