fs/cpio: generate reproducible archives

The output of 'find' depends on the directory entries, and is not
ordered. As a consequence, the cpio archive is not reproducible.

Fix that by sorting the output of find. Use the 'C' locale to enforce
reproducibility that does not depend on the locale.

The command line is now pretty long, so we wrap it.

Signed-off-by: Yurii Monakov <monakov.y@gmail.com>
[yann.morin.1998@free.fr:
  - use LC_ALL=C when sorting
  - wrap long line
  - reword commit log
]
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>

fs/cpio/cpio.mk

@@ -37,7 +37,11 @@ ROOTFS_CPIO_OPTS += --reproducible
 endif
 
 define ROOTFS_CPIO_CMD
-	cd $(TARGET_DIR) && find . | cpio $(ROOTFS_CPIO_OPTS) --quiet -o -H newc > $@
+	cd $(TARGET_DIR) && \
+	find . \
+	| LC_ALL=C sort \
+	| cpio $(ROOTFS_CPIO_OPTS) --quiet -o -H newc \
+	> $@
 endef
 
 ifeq ($(BR2_TARGET_ROOTFS_CPIO_UIMAGE),y)