CI/BM: fix BuildCheck — pin ubuntu-24.04, upgrade DDT image to gcc-14, register rasdaemon/mce-inject submodules, gate warnings via allowlist

[hongyuni]

Summary

Restore the open-source BuildCheck CI job to a working state. The previous
configuration depended on a personal fork submodule, an outdated gcc-13 image,
a buggy build_check script, and a ubuntu-latest runner whose silent shift to
24.04 was already exposing pre-existing build warnings as job failures.

What's in this PR

1. BM/ras: add rasdaemon and mce-inject submodules, re-pin mce-test
   .gitmodules is updated to point mce-test at the canonical upstream
   (git.kernel.org/.../mce-test.git) and re-pinned to dbbbc64 (reachable
   in upstream master). rasdaemon (github.com/mchehab/rasdaemon @ a4620eb)
   and mce-inject (git.kernel.org/.../mce-inject @ ca81c1d) are added as
   first-class submodules so actions/checkout --recurse-submodules populates
   them on every CI run. All three SHAs verified reachable from upstream.

2. BM/ras: refresh Makefile, tests and helper scripts
   Pure content sync of the per-test shell scripts (mce_test.sh,
   lmce_test.sh, ras_common.sh), the per-subdir Makefile, the README,
   and adds bff_test.sh / einjv2_test.sh. No CI / build-system changes
   in this commit.

3. BM: bump Dockerfile.build.ddt to gcc-14 and add rasdaemon build deps
   New BM/ras subdirs (cmpccxadd and others) need gcc >= 14. Image base
   stays at ubuntu:24.04 (gcc-14 is in noble universe, no PPA required).
   Adds bison, flex, autoconf, automake, libtool, pkg-config,
   libsqlite3-dev, libtraceevent-dev, python3 so rasdaemon can
   autoreconf && ./configure --enable-sqlite3 --enable-mce …. Registers
   gcc-14/g++-14 via update-alternatives so bare gcc/g++ resolves to
   v14 without touching in-tree Makefiles.

4. BM/Makefile: add DDT_SKIP_SUBDIRS skip mechanism and fix failure detection
   Adds an opt-in skip list (used by CI to skip tdx-compliance, which
   needs a matching /lib/modules/$(uname -r)/build tree not available in
   the runner). Fixes a latent bug in the post-build error check that
   inspected an undefined MAKE_TOOLS_LOG instead of MAKE_LKVS_LOG,
   masking real subdir build failures. Mounts /lib/modules into
   docker_clean/docker_make to match docker_make_ddt, and adds a
   matching docker_clean_ddt target.

5. ci: pin ubuntu-24.04, build with gcc-14 DDT image, gate warnings via allowlist

   • runs-on: ubuntu-latest → ubuntu-24.04 on every job (pin, not float).
   • BuildCheck builds from BM/Dockerfile.build.ddt (gcc-14) instead of
     BM/Dockerfile.build (gcc-11) and drops the docker-engine bootstrap
     block (Docker is preinstalled on GitHub-hosted runners) plus sudo -E.
   • actions/checkout v3 → v4 with submodules: recursive;
     actions/setup-python v4 → v5.
   • cfg-lint-check replaces the third-party tj-actions/changed-files@v46
     with an inline git diff --diff-filter=ACMRT over the PR merge-base.
   • build_check is rewritten: named/cleanup-trapped container, toolchain
     diagnostic step, rasdaemon preconfigure, tdx-compliance skip via
     DDT_SKIP_SUBDIRS, and a new
     .github/scripts/build_warning_allowlist (regex per line) so only
     new warnings fail the job. Existing entries should be pruned as the
     underlying sources are fixed; this is not a forever-suppress mechanism.