user/bcachefs-tools: add bcachefs-tools-ckms submodule, update to 1.34.0

[leroycep]

Description

This PR updates bcachefs-tools to version 1.34.0 and adds a user/bcachefs-tools-ckms subpackage.

This is the same as #4863, but rebased on master and with a commit updating it to 1.34.0 (and also a commit updating to 1.31.12 that I never got around to submitting). I also changed the git branch name from bcachefs-1.31.7-ckms to user-bcachefs-tools-ckms.

I'm submitting this update because bcachefs-tools-ckms 1.31.12 doesn't compile for linux 6.18. After these changes I was able to compile the kernel module and reboot desktop computer. I will be testing it on my laptop shortly.

Currently there are two patches to the bcachefs-tools source code:

1. A patch that fixes non-portable usage of sed and find in the Makefile.
2. A patch to a header file replacing a macro's call to strlen with __builtin_strlen. Without the patch I get an error about compile-time constants:

libbcachefs/fs/check.c:113:36: error: initializer element is not a compile-time constant
  113 | static struct qstr lostfound_str = QSTR("lost+found");
      |                                    ^
include/linux/dcache.h:15:30: note: expanded from macro 'QSTR'
   15 | #define QSTR(n) (struct qstr)QSTR_INIT(n, strlen(n))
      |                              ^
include/linux/kernel.h:253:26: note: expanded from macro 'QSTR_INIT'
  253 | #define QSTR_INIT(n,l) { { { .len = l } }, .name = n }
      |                          ^
1 error generated.

I'm assuming that this comes down to a difference between how gcc and clang handle strlen.

Checklist

Before this pull request is reviewed, certain conditions must be met.

The following must be true for all changes:

• I have read CONTRIBUTING.md
• I acknowledge that overtly not following the above or the below will result in my pull request getting closed

The following must be true for template/package changes:

• I have read Packaging.md
• I have built and tested my changes on my machine