lib: Add CRC32-C

This is needed for BTRFS.

Signed-off-by: Marek Behun <marek.behun@nic.cz>

 create mode 100644 lib/crc32c.c
diff --git a/lib/Makefile b/lib/Makefile
index 8e1c9d1..80216c2 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -71,6 +71,7 @@
 CFLAGS_display_options.o := $(if $(BUILD_TAG),-DBUILD_TAG='"$(BUILD_TAG)"')
 obj-$(CONFIG_BCH) += bch.o
 obj-y += crc32.o
+obj-$(CONFIG_CRC32C) += crc32c.o
 obj-y += ctype.o
 obj-y += div64.o
 obj-y += hang.o