package/containerd: fix btrfs handling

btrfs handling doesn't depend on btrfs-progs but on kernel >= 4.12 since
bump to version 1.7.7 in commit 79e01ef9506a6cdc4836912607dc594ae7b1999d
and
https://github.com/containerd/containerd/commit/024a748c092cbddde0918f2e93a646ce50116e11
resulting in the following build failure:

In file included from vendor/github.com/containerd/btrfs/v2/btrfs.go:21:0:
./btrfs.h:19:2: error: #error "Headers from kernel >= 4.12 are required on compilation time (not on run time)"
 #error "Headers from kernel >= 4.12 are required on compilation time (not on run time)"
  ^~~~~
In file included from vendor/github.com/containerd/btrfs/v2/btrfs.go:21:0:
./btrfs.h:22:10: fatal error: linux/btrfs_tree.h: No such file or directory
 #include <linux/btrfs_tree.h>
          ^~~~~~~~~~~~~~~~~~~~

Fixes: 79e01ef9506a6cdc4836912607dc594ae7b1999d
 - http://autobuild.buildroot.org/results/d6afeef47daae1783dcce3e2b6a0a16e3e5d5fbd

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/containerd/Config.in

@@ -20,12 +20,13 @@ if BR2_PACKAGE_CONTAINERD
 
 config BR2_PACKAGE_CONTAINERD_DRIVER_BTRFS
 	bool "btrfs snapshot driver"
-	depends on BR2_USE_MMU # btrfs-progs
-	depends on BR2_TOOLCHAIN_HAS_THREADS # btrfs-progs
-	select BR2_PACKAGE_BTRFS_PROGS
+	depends on BR2_TOOLCHAIN_HEADERS_AT_LEAST_4_12
 	help
 	  Build the btrfs snapshot driver for containerd.
 
+comment "brtfs snapshot driver needs headers >= 4.12"
+	depends on !BR2_TOOLCHAIN_HEADERS_AT_LEAST_4_12
+
 config BR2_PACKAGE_CONTAINERD_DRIVER_DEVMAPPER
 	bool "devmapper snapshot driver"
 	depends on BR2_TOOLCHAIN_HAS_THREADS # lvm2

package/containerd/containerd.mk

@@ -35,9 +35,7 @@ CONTAINERD_DEPENDENCIES += libseccomp host-pkgconf
 CONTAINERD_TAGS += seccomp
 endif
 
-ifeq ($(BR2_PACKAGE_CONTAINERD_DRIVER_BTRFS),y)
-CONTAINERD_DEPENDENCIES += btrfs-progs
-else
+ifneq ($(BR2_PACKAGE_CONTAINERD_DRIVER_BTRFS),y)
 CONTAINERD_TAGS += no_btrfs
 endif