Build a minimized Nix with MinGW

At this point many features are stripped out, but this works:

- Can run libnix{util,store,expr} unit tests
- Can run some Nix commands

Co-Authored-By volth <volth@volth.com>
Co-Authored-By Brian McKenna <brian@brianmckenna.org>

src/libstore/build/substitution-goal.hh

@@ -1,125 +0,0 @@
-#pragma once
-///@file
-
-#include "lock.hh"
-#include "store-api.hh"
-#include "goal.hh"
-
-namespace nix {
-
-class Worker;
-
-struct PathSubstitutionGoal : public Goal
-{
-    /**
-     * The store path that should be realised through a substitute.
-     */
-    StorePath storePath;
-
-    /**
-     * The path the substituter refers to the path as. This will be
-     * different when the stores have different names.
-     */
-    std::optional<StorePath> subPath;
-
-    /**
-     * The remaining substituters.
-     */
-    std::list<ref<Store>> subs;
-
-    /**
-     * The current substituter.
-     */
-    std::shared_ptr<Store> sub;
-
-    /**
-     * Whether a substituter failed.
-     */
-    bool substituterFailed = false;
-
-    /**
-     * Path info returned by the substituter's query info operation.
-     */
-    std::shared_ptr<const ValidPathInfo> info;
-
-    /**
-     * Pipe for the substituter's standard output.
-     */
-    Pipe outPipe;
-
-    /**
-     * The substituter thread.
-     */
-    std::thread thr;
-
-    std::promise<void> promise;
-
-    /**
-     * Whether to try to repair a valid path.
-     */
-    RepairFlag repair;
-
-    /**
-     * Location where we're downloading the substitute.  Differs from
-     * storePath when doing a repair.
-     */
-    Path destPath;
-
-    std::unique_ptr<MaintainCount<uint64_t>> maintainExpectedSubstitutions,
-        maintainRunningSubstitutions, maintainExpectedNar, maintainExpectedDownload;
-
-    typedef void (PathSubstitutionGoal::*GoalState)();
-    GoalState state;
-
-    /**
-     * Content address for recomputing store path
-     */
-    std::optional<ContentAddress> ca;
-
-    void done(
-        ExitCode result,
-        BuildResult::Status status,
-        std::optional<std::string> errorMsg = {});
-
-public:
-    PathSubstitutionGoal(const StorePath & storePath, Worker & worker, RepairFlag repair = NoRepair, std::optional<ContentAddress> ca = std::nullopt);
-    ~PathSubstitutionGoal();
-
-    void timedOut(Error && ex) override { abort(); };
-
-    /**
-     * We prepend "a$" to the key name to ensure substitution goals
-     * happen before derivation goals.
-     */
-    std::string key() override
-    {
-        return "a$" + std::string(storePath.name()) + "$" + worker.store.printStorePath(storePath);
-    }
-
-    void work() override;
-
-    /**
-     * The states.
-     */
-    void init();
-    void tryNext();
-    void gotInfo();
-    void referencesValid();
-    void tryToRun();
-    void finished();
-
-    /**
-     * Callback used by the worker to write to the log.
-     */
-    void handleChildOutput(int fd, std::string_view data) override;
-    void handleEOF(int fd) override;
-
-    /* Called by destructor, can't be overridden */
-    void cleanup() override final;
-
-    JobCategory jobCategory() const override {
-        return JobCategory::Substitution;
-    };
-};
-
-}