ioctl: add decoding support for btrfs ioctls

* btrfs.c: New file.
* file_ioctl.c: Likewise.
* Makefile.am (strace_SOURCES): Add them.
* configure.ac (AC_CHECK_HEADERS): Add linux/btrfs.h.
(AC_CHECK_MEMBERS): Add struct btrfs_ioctl_feature_flags.compat_flags,
struct btrfs_ioctl_fs_info_args.nodesize,
struct btrfs_ioctl_defrag_range_args.start,
and struct btrfs_ioctl_search_args_v2.buf_size.
(AC_CHECK_DECLS): Add BTRFS_COMPRESS_* enums.
* defs.h (btrfs_ioctl, file_ioctl): New prototypes.
* ioctl.c (ioctl_decode) [HAVE_LINUX_BTRFS_H]: Use btrfs_ioctl.
* xlat/btrfs_balance_args.in: New file.
* xlat/btrfs_balance_ctl_cmds.in: Likewise.
* xlat/btrfs_balance_flags.in: Likewise.
* xlat/btrfs_balance_state.in: Likewise.
* xlat/btrfs_compress_types.in: Likewise.
* xlat/btrfs_defrag_flags.in: Likewise.
* xlat/btrfs_dev_replace_cmds.in: Likewise.
* xlat/btrfs_dev_replace_results.in: Likewise.
* xlat/btrfs_dev_replace_state.in: Likewise.
* xlat/btrfs_dev_stats_flags.in: Likewise.
* xlat/btrfs_dev_stats_values.in: Likewise.
* xlat/btrfs_features_compat.in: Likewise.
* xlat/btrfs_features_compat_ro.in: Likewise.
* xlat/btrfs_features_incompat.in: Likewise.
* xlat/btrfs_key_types.in: Likewise.
* xlat/btrfs_qgroup_ctl_cmds.in: Likewise.
* xlat/btrfs_qgroup_inherit_flags.in: Likewise.
* xlat/btrfs_qgroup_limit_flags.in: Likewise.
* xlat/btrfs_qgroup_status_flags.in: Likewise.
* xlat/btrfs_scrub_flags.in: Likewise.
* xlat/btrfs_send_flags.in: Likewise.
* xlat/btrfs_snap_flags_v2.in: Likewise.
* xlat/btrfs_space_info_flags.in: Likewise.
* xlat/btrfs_tree_objectids.in: Likewise.
diff --git a/ioctl.c b/ioctl.c
index 1b69e97..d82af4b 100644
--- a/ioctl.c
+++ b/ioctl.c
@@ -267,6 +267,10 @@
 	case 0xaa:
 		return uffdio_ioctl(tcp, code, arg);
 #endif
+#ifdef HAVE_LINUX_BTRFS_H
+	case 0x94:
+		return btrfs_ioctl(tcp, code, arg);
+#endif
 	default:
 		break;
 	}