squashfs: do not force gzip support if lz4/xz/zstd is selected

The logic to ensure at least one compression backend is selected was not
updated when lz4, xz and zstd were introduced -  Fix that.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
Reviewed-by: Peter Seiderer <ps.report@gmx.net>
[Peter: add comment as suggested by Peter Seiderer]
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

(cherry picked from commit 84aeb4419f394b2eb11a22a962bc20e05b311b5f)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/squashfs/Config.in

@@ -2,7 +2,13 @@ config BR2_PACKAGE_SQUASHFS
 	bool "squashfs"
 	depends on BR2_TOOLCHAIN_HAS_THREADS
 	depends on BR2_USE_MMU # fork()
-	select BR2_PACKAGE_SQUASHFS_GZIP if !(BR2_PACKAGE_SQUASHFS_LZMA || BR2_PACKAGE_SQUASHFS_LZO)
+	# ensure at least on compression backend (defaults to gzip)
+	select BR2_PACKAGE_SQUASHFS_GZIP if !( \
+	       BR2_PACKAGE_SQUASHFS_LZ4 || \
+	       BR2_PACKAGE_SQUASHFS_LZMA || \
+	       BR2_PACKAGE_SQUASHFS_LZO || \
+	       BR2_PACKAGE_SQUASHFS_XZ || \
+	       BR2_PACKAGE_SQUASHFS_ZSTD)
 	help
 	  Tools to generate SquashFS filesystems.