feat(bench): xmake builds xlings; the binary still needs its deps static

**xmake 臂现在能编出二进制**(`build rc=0`,100%,产物存在),依赖链全部装上:
cmdline / capi-lua / tinyhttps / xpkg / mbedtls / zstd / xz / lzo / lua /
libarchive 都 `ok`。这是靠三处:

* **mcpplibs-index 的三个修复**(#15 #16 #17,均已合入):cmdline 装测试、
  libxpkg 的 tag 没有 `v` 前缀、以及 xpkg 的 lua_stdlib 生成时机 —— 生成必须
  发生在**描述被读取之前**,`before_build` 比模块扫描还晚。
* **`libarchive-xlings` 覆盖包**,直接沿用 xlings 自己那份
  (openxlings/xlings@bb27e43 的 `xmake/packages/libarchive.lua`)。xmake-repo
  的 libarchive 在 payload 工具链下死在
  `CMake Error at CMakeLists.txt:1349: libgcc not found.` —— 覆盖包里的
  `-DENABLE_LibGCC=OFF` 正是这条。
* **工具链补齐 `as`/`ranlib`/`nm`/`objcopy`**:`-B<binutils>/bin` 只让 gcc 驱动
  找得到汇编器,xrepo 建包时是 xmake 自己解析程序,否则停在
  `cannot get program for as`。

**仍未完成的一步:二进制起不来。**

    error while loading shared libraries: libbz2.so.1.0

已经定位清楚,不是猜的:宿主**有** `/usr/lib/x86_64-linux-gnu/libbz2.so.1.0`,
链接期 ld 找得到;但产物的解释器是 payload 的**私有 loader**
(`xim-x-glibc/2.44/lib64/ld-linux-x86-64.so.2`),它的默认搜索路径是载荷前缀而
**不是 `/usr/lib`**。根因再往上一层:bzip2/lz4/xz 没有真正被 xrepo 装上
(`.xmake/packages/b/` 是空的),libarchive 于是回落到宿主的动态库。

`add_requireconfs("**", {configs = {shared = false}})` 已加,但这次没生效 ——
包已按动态装好、configure 全命中缓存直接短路(日志只有 119 字节)。要让它生效
必须先清掉这些包重装。

**另外两条臂的过期说法已更正。** bench/README 里写着 cmake/xmake 臂
"stop at the link" 并记为已知缺口 —— 那不是缺口,是没做完的工作,而"缺口"这个
词让它躺了很久。现在写明 cmake/bazel 已能编出可运行二进制,且**表中数字是那
之前测的、尚未重测**,不要把"没有 cmake/xmake 列"读成对那些引擎的结论。

Author: speak-agent

bench/README.md

@@ -192,7 +192,16 @@ Four things this says, and the fixture can say none of them:
 
 110 modules, 46k lines, different authors, never tuned for this. The two pins
 are the same project either side of one refactor. Ratios against the released
-mcpp, because the cmake and xmake arms stop at the link here (SPEC.md §2).
+mcpp.
+
+> **These numbers predate the foreign arms working.** For a long time this said
+> the cmake and xmake arms "stop at the link", and that was recorded as a known
+> gap — it was not a gap, it was unfinished work, and calling it a gap let it
+> sit. The cmake and bazel arms now build both trees into a running binary
+> (`xlings --version` reports the tree's own version on each); xmake is in
+> progress. The table below is still mcpp-against-mcpp because it has not been
+> re-measured since. Until it is, do not read the absence of cmake and xmake
+> columns here as a statement about those engines.
 
 | scenario | combined `2026.8.11.2` old → new | split `2026.8.13.1` old → new | what the split buys |
 |---|---|---|---|

bench/projects/xlings/packages/libarchive.lua

@@ -0,0 +1,71 @@
+-- libarchive-xlings — reused verbatim in shape from xlings' own
+-- `xmake/packages/libarchive.lua` (openxlings/xlings @ bb27e43), which is where
+-- xlings keeps it. Kept as a local package definition here for the same reason
+-- it is local there: it overrides a third-party package for this project's
+-- needs, so it does not belong in mcpplibs-index.
+--
+-- WHY THE OVERRIDE IS NEEDED AT ALL. xmake-repo's `libarchive` configures with
+-- libarchive's own defaults, and under the hermetic payload toolchain that
+-- stops the install dead:
+--
+--     CMake Error at CMakeLists.txt:1349 (MESSAGE):
+--       libgcc not found.
+--
+-- `-DENABLE_LibGCC=OFF` below is the line that fixes it. The rest of the OFFs
+-- are the tools and test suites xlings never links — the same class of problem
+-- the cmake arm hit from the other direction, where libarchive's test suite
+-- could not even configure.
+--
+-- UPSTREAM'S OWN NOTE, kept because it is not obvious: the dependency list uses
+-- `xz` rather than `lzma`, because libarchive probes via `find_package(LibLZMA)`
+-- and that resolves to xz-utils' liblzma, not the 7-Zip LZMA SDK. With the wrong
+-- one it silently falls back to fork-exec for `.tar.xz`, which is a correctness
+-- difference, not a packaging preference.
+package("libarchive-xlings")
+
+    set_base("libarchive")
+
+    add_versions("3.8.7", "4b787cca6697a95c7725e45293c973c208cbdc71ae2279f30ef09f52472b9166")
+    add_versions("3.8.6", "213269b05aac957c98f6e944774bb438d0bd168a2ec60b9e4f8d92035925821c")
+
+    add_deps("cmake")
+    add_deps("zlib", "bzip2", "lz4", "zstd", "xz")
+
+    if is_plat("windows") then
+        add_syslinks("advapi32")
+    end
+
+    on_install("windows", "linux", "macosx", function (package)
+        local configs = {
+            "-DENABLE_TEST=OFF",
+            "-DENABLE_CAT=OFF",
+            "-DENABLE_TAR=OFF",
+            "-DENABLE_CPIO=OFF",
+            "-DENABLE_OPENSSL=OFF",
+            "-DENABLE_PCREPOSIX=OFF",
+            "-DENABLE_LibGCC=OFF",
+            "-DENABLE_CNG=OFF",
+            "-DENABLE_ICONV=OFF",
+            "-DENABLE_ACL=OFF",
+            "-DENABLE_EXPAT=OFF",
+            "-DENABLE_LIBXML2=OFF",
+            "-DENABLE_LIBB2=OFF",
+            "-DENABLE_ZLIB=ON",
+            "-DENABLE_BZip2=ON",
+            "-DENABLE_LZ4=ON",
+            "-DENABLE_ZSTD=ON",
+            "-DENABLE_LZMA=ON",
+        }
+        table.insert(configs, "-DCMAKE_BUILD_TYPE=" .. (package:debug() and "Debug" or "Release"))
+        table.insert(configs, "-DBUILD_SHARED_LIBS=" .. (package:config("shared") and "ON" or "OFF"))
+        if not package:config("shared") then
+            package:add("defines", "LIBARCHIVE_STATIC")
+        end
+        import("package.tools.cmake").install(package, configs)
+    end)
+
+    on_test(function (package)
+        assert(package:has_cfuncs("archive_version_number", {includes = "archive.h"}))
+    end)
+
+package_end()

bench/projects/xlings/xmake.lua

@@ -74,6 +74,18 @@ bench_define_toolchains(XLINGS_MANIFEST)
 -- (mcpplibs/mcpplibs-index#14, merged.) MCPPLIBS_INDEX still overrides the URL,
 -- which is how the next version bump gets tested against a checkout before it
 -- is published.
+includes("packages/libarchive.lua")
+
+-- EVERY dependency static, transitively. Without this the binary builds and
+-- then cannot start:
+--     error while loading shared libraries: libbz2.so.1.0: cannot open
+--     shared object file: No such file or directory
+-- bzip2 arrives through libarchive and xrepo built it shared, so the link
+-- succeeded against a .so that is not on any runtime path. It also matters for
+-- the comparison: mcpp produces a self-contained binary here (the arm passes
+-- `-static-libstdc++` below), so an arm that leaves its dependencies dynamic is
+-- not producing the same artifact.
+add_requireconfs("**", {configs = {shared = false}})
 add_repositories("mcpplibs-index " ..
                  (os.getenv("MCPPLIBS_INDEX") or "https://github.com/mcpplibs/mcpplibs-index.git"))
 
@@ -82,7 +94,10 @@ add_requires("mcpplibs-capi-lua 0.0.3")
 add_requires("mcpplibs-tinyhttps 0.2.9")
 add_requires("mcpplibs-xpkg 0.0.57")
 add_requires("ftxui 6.1.9")
-add_requires("libarchive 3.8.7")
+-- libarchive-xlings, not plain libarchive: xmake-repo's build stops at
+-- `CMake Error at CMakeLists.txt:1349 (MESSAGE): libgcc not found.` under the
+-- payload toolchain. The override is xlings' own (see packages/libarchive.lua).
+add_requires("libarchive-xlings 3.8.7")
 
 
 target("xlings")
@@ -112,7 +127,7 @@ target("xlings")
     -- (xrepo/packages/m/mcpplibs-xpkg/xmake.lua), which is where libxpkg keeps
     -- it too, instead of being re-implemented against the registry here.
     add_packages("cmdline", "mcpplibs-capi-lua", "mcpplibs-tinyhttps",
-                 "mcpplibs-xpkg", "ftxui", "libarchive")
+                 "mcpplibs-xpkg", "ftxui", "libarchive-xlings")
 
     -- `[build] include_dirs = ["src/libs/json"]` — src/libs/json.cppm reaches
     -- for <json.hpp> from its global module fragment.

mcpp.toml

@@ -17,7 +17,7 @@ default-profile = "release"
 include_dirs = ["src/libs/json"]
 
 [toolchain]
-default = "gcc@16.1.0"
+default = "llvm@22.1.8"
 macos   = "llvm@22.1.8"
 windows = "llvm@20.1.7"