fix(dist): 产物格式的判据匹配不到 mcpp 自己用的三元组拼法

    if (t.find("apple")) return MachO;

apple / darwin 是 LLVM 的词。mcpp 的规范形式是 aarch64-macos,两个都不含 —— 于是
这个判断在**每一种宿主上**都落到了「问宿主」,而它产生的两种失败方向相反:

    Linux 宿主 + macOS 目标   → 给 Mach-O 用了 Elf 的契约
    macOS 宿主 + Linux 目标   → 给 ELF 用了 MachO 的契约

⚠️ 实测第二种(macOS runner 交叉到 x86_64-linux-gnu):

    ld.lld: error: unable to find library -load_hidden
    …/xim-x-llvm/22.1.8/lib/libc++.a: archive member 'system_error.cpp.o'
      is neither ET_REL nor LLVM bitcode

-load_hidden 是 Mach-O 链接器的词,那个归档是**宿主的** —— 两个都是因为「格式」
这个问题被用「哪台机器在构建」回答了。

⇒ 先用已解析的 triple 回答(is_pe / os == macos / linux / none);字符串判断保留
在后面,作为词表解析不了的三元组([target.X] 逃生口)的兜底,那里只有拼法可依。

Author: speak-agent

src/build/flags.cppm

@@ -914,6 +914,37 @@ CompileFlags compute_flags(const BuildPlan& plan) {
             // Only ADDS answers: a triple that says neither falls through to
             // exactly the previous derivation, so no existing build changes.
             const auto& t = plan.toolchain.targetTriple;
+            // ⭐⭐ THE PARSED TRIPLE FIRST, BECAUSE THE SUBSTRINGS BELOW DO NOT
+            // MATCH THE SPELLING mcpp ITSELF USES.
+            //
+            // `apple` and `darwin` are LLVM's words. mcpp's canonical form for
+            // that target is `aarch64-macos`, which contains neither — so the
+            // test fell through to the host on every host, and the two failures
+            // that produces are opposite:
+            //
+            //   Linux host, macOS target    → Elf contract for a Mach-O
+            //   macOS host, Linux target    → MachO contract for an ELF
+            //
+            // ⚠️ Measured 2026-08-23, the second one, on a macOS runner
+            // cross-building for `x86_64-linux-gnu` over openkal:
+            //
+            //     ld.lld: error: unable to find library -load_hidden
+            //     …/xim-x-llvm/22.1.8/lib/libc++.a: archive member
+            //       'system_error.cpp.o' is neither ET_REL nor LLVM bitcode
+            //
+            // `-load_hidden` is a Mach-O linker's word and that archive is the
+            // HOST's — both chosen because the format question was answered by
+            // asking which machine was doing the building.
+            //
+            // The substring tests are kept below as a fallback for a triple the
+            // vocabulary cannot parse (the `[target.X]` escape hatch), where a
+            // spelling is all there is.
+            if (auto parsed = mcpp::toolchain::triple::parse(t)) {
+                if (parsed->is_pe())            return dist::Format::Pe;
+                if (parsed->os == "macos")      return dist::Format::MachO;
+                if (parsed->os == "linux"
+                    || parsed->os == "none")    return dist::Format::Elf;
+            }
             if (t.find("windows") != std::string::npos
                 || t.find("mingw") != std::string::npos)
                 return dist::Format::Pe;