squashfs: Add lz4 hc compression

lz4 offers a high compression mode. A minimalistic file system shrinks by about 15%.

[Peter: Unconditionally use hc mode for lz4 instead of introducing another option]
Signed-off-by: Matthias Weisser <m.weisser.m@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

fs/squashfs/squashfs.mk

@@ -7,7 +7,7 @@
 ROOTFS_SQUASHFS_DEPENDENCIES = host-squashfs
 
 ifeq ($(BR2_TARGET_ROOTFS_SQUASHFS4_LZ4),y)
-ROOTFS_SQUASHFS_ARGS += -comp lz4
+ROOTFS_SQUASHFS_ARGS += -comp lz4 -Xhc
 else
 ifeq ($(BR2_TARGET_ROOTFS_SQUASHFS4_LZO),y)
 ROOTFS_SQUASHFS_ARGS += -comp lzo