fix: rebuild and relink on what changed, submodules at their revisions, and mingw found where it is

- Shaders record the files glslang opened (a depfile) and their settings
  (source path, stage, entry point, defines, include directories) in the
  build directory, and rebuild when an included file or a setting changes,
  not only the shader's own source.
- An executable relinks when its link command changed, not only when an
  object is newer: a link flag in project.cpp, or a dependency's library
  that moved (an ExternalDependency built into a new cache directory). The
  command is recorded beside the objects; its flags come from ordered sets,
  so the order the dependency threads finish in can't change it.
- An external's newest artifact counts its libDirs and versioned .so names.
- Submodules are checked out at the revisions the fetched commit records,
  from the URLs its .gitmodules gives, after every clone, switch, checkout
  and pull, so a pinned commit builds against its own submodules, and one
  moved by hand is put back; with no .gitmodules, git isn't asked.
- Each external clone's fetch and build hold a file lock: parallel builds
  pulled into one clone at once ("cannot lock ref").
- mingw:
  - -stdlib=libstdc++ always;
  - the std module's source is found through libstdc++.modules.json in the
    mingw toolchain's own library directories (the generic lib/ holds the
    host's Linux one), asking the compiler once a run;
  - a toolchain that isn't there is a build error saying where it looked,
    not std::terminate;
  - CRAFTER_MINGW_DIR names the prefix, the directory holding
    x86_64-w64-mingw32/ and lib/gcc/;
  - inside the Flatpak the host's /usr mingw is used.
- RunScript's exit-status check reads as the one range it is.
- Tests: ConcurrentExternalFetch, ExternalArtifactTime, GitSubmodules,
  LinkFlagsChange, MingwMissing, ShaderIncludeChange; ShaderCompile and
  ToolchainResolve extended.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/LinkFlagsChange/fixture/main.cpp

@@ -0,0 +1,6 @@
+// SPDX-License-Identifier: LGPL-3.0-only
+// SPDX-FileCopyrightText: Copyright (C) 2026 Catcrafts®
+
+int main() {
+    return 0;
+}

tests/LinkFlagsChange/main.cpp

@@ -0,0 +1,119 @@
+// SPDX-License-Identifier: LGPL-3.0-only
+// SPDX-FileCopyrightText: Copyright (C) 2026 Catcrafts®
+
+import std;
+import Crafter.Build;
+namespace fs = std::filesystem;
+using namespace Crafter;
+
+// A change to what an executable is linked with has to relink it, even when
+// no object changed. The relink check compared modification times only, so a
+// link flag added in project.cpp, or a dependency's library moving (an
+// ExternalDependency whose options changed is fetched and built into a new
+// cache directory, and its -L and rpath follow), left the old binary in
+// place: Crafter.Network's tests kept loading the msquic they were first
+// linked against.
+//
+// The test adds an rpath to an executable's link flags, takes it away again,
+// and then builds once more with nothing changed, which must not relink.
+// The flags come out of sets the dependency threads fill as they finish, so
+// the recorded command lists them sorted: in the order they happened to land
+// in, an unchanged build could look like a changed one.
+
+namespace {
+    std::int32_t failures = 0;
+
+    void Check(bool cond, std::string_view msg) {
+        if (!cond) {
+            std::println(std::cerr, "FAIL: {}", msg);
+            ++failures;
+        }
+    }
+
+    constexpr std::string_view marker = "/crafter-build-link-flags-change-marker";
+
+    BuildResult BuildOnce(const fs::path& project, std::vector<std::string> linkFlags) {
+        Configuration app;
+        app.path = project;
+        app.name = "linked";
+        app.outputName = "linked";
+        app.target = HostTarget();
+        app.type = ConfigurationType::Executable;
+        app.linkFlags = std::move(linkFlags);
+        std::array<fs::path, 0> ifaces = {};
+        std::array<fs::path, 1> impls = { "main" };
+        app.GetInterfacesAndImplementations(ifaces, impls);
+        std::unordered_map<fs::path, std::shared_future<BuildResult>> depResults;
+        std::mutex depMutex;
+        BuildResult result = Build(app, depResults, depMutex);
+        return result;
+    }
+
+    Configuration Plain(const fs::path& project) {
+        Configuration app;
+        app.path = project;
+        app.name = "linked";
+        app.outputName = "linked";
+        app.target = HostTarget();
+        app.type = ConfigurationType::Executable;
+        return app;
+    }
+
+    fs::path Binary(const fs::path& project) {
+        return Plain(project).BinDir() / "linked";
+    }
+
+    bool HasMarker(const fs::path& binary) {
+        std::ifstream stream(binary, std::ios::binary);
+        const std::string bytes((std::istreambuf_iterator<char>(stream)), std::istreambuf_iterator<char>());
+        return bytes.find(marker) != std::string::npos;
+    }
+}
+
+int main() {
+    const fs::path project = fs::temp_directory_path() / "crafter-build-link-flags-change";
+    fs::remove_all(project);
+    fs::copy(fs::current_path() / "tests" / "LinkFlagsChange" / "fixture", project, fs::copy_options::recursive);
+    const std::string rpath = std::format("-Wl,-rpath,{}", marker);
+
+    const BuildResult first = BuildOnce(project, {});
+    Check(first.result.empty(), std::format("the plain build succeeds: {}", first.result));
+    const fs::path binary = Binary(project);
+    Check(fs::exists(binary) && !HasMarker(binary), "the plain binary has no rpath to the marker");
+
+    const BuildResult added = BuildOnce(project, { rpath });
+    Check(added.result.empty(), std::format("the build with the rpath succeeds: {}", added.result));
+    Check(HasMarker(binary), "adding a link flag relinks the binary");
+
+    const BuildResult removed = BuildOnce(project, {});
+    Check(removed.result.empty(), std::format("the build without it succeeds: {}", removed.result));
+    Check(!HasMarker(binary), "taking it away relinks it again");
+
+    const fs::file_time_type linked = fs::last_write_time(binary);
+    const BuildResult again = BuildOnce(project, {});
+    Check(again.result.empty() && fs::last_write_time(binary) == linked, "an unchanged build doesn't relink");
+
+    const std::vector<std::string> flags = { "-Wl,-z,now", "-Wl,-O1", "-Wl,--as-needed", "-Wl,-z,relro", "-Wl,--build-id", "-Wl,--hash-style=gnu" };
+    const BuildResult many = BuildOnce(project, flags);
+    Check(many.result.empty(), std::format("the build with six flags succeeds: {}", many.result));
+    std::ifstream recorded(Plain(project).BuildDir() / "linked.link", std::ios::binary);
+    const std::string record((std::istreambuf_iterator<char>(recorded)), std::istreambuf_iterator<char>());
+    std::vector<std::size_t> at;
+    for (const std::string& flag : flags) at.push_back(record.find(std::format(" {}", flag)));
+    std::vector<std::string> sorted = flags;
+    std::ranges::sort(sorted);
+    bool inOrder = !std::ranges::contains(at, std::string::npos);
+    for (std::size_t k = 0; inOrder && k + 1 < sorted.size(); ++k) {
+        const auto index = [&](const std::string& flag) { return at[static_cast<std::size_t>(std::ranges::find(flags, flag) - flags.begin())]; };
+        inOrder = index(sorted[k]) < index(sorted[k + 1]);
+    }
+    Check(inOrder, std::format("the link record lists the flags sorted: {}", record));
+
+    std::error_code ec;
+    fs::remove_all(project, ec);
+    if (failures > 0) {
+        std::println(std::cerr, "{} assertions failed", failures);
+        return 1;
+    }
+    return 0;
+}