[goalc] add a build system (#704)

* add first attempt at build system

* fix stupid bug

* try again

goalc/make/Tool.cpp

@@ -0,0 +1,59 @@
+
+#include <chrono>
+#include <filesystem>
+
+#include "third-party/fmt/core.h"
+
+#include "Tool.h"
+#include "common/util/FileUtil.h"
+
+Tool::Tool(const std::string& name) : m_name(name) {}
+
+bool Tool::needs_run(const ToolInput& task) {
+  // for this to return false, all outputs need to be newer than all inputs.
+
+  auto in_file = std::filesystem::path(file_util::get_file_path({task.input}));
+
+  if (!std::filesystem::exists(in_file)) {
+    throw std::runtime_error(fmt::format("Input file {} does not exist.", task.input));
+  }
+
+  auto newest_input = std::filesystem::last_write_time(in_file);
+  for (auto& dep : task.deps) {
+    auto dep_path = std::filesystem::path(file_util::get_file_path({dep}));
+    if (std::filesystem::exists(dep_path)) {
+      auto dep_time = std::filesystem::last_write_time(dep_path);
+      if (dep_time > newest_input) {
+        newest_input = dep_time;
+      }
+    } else {
+      return true;  // don't have a dep.
+    }
+  }
+
+  for (auto& dep : get_additional_dependencies(task)) {
+    auto dep_path = std::filesystem::path(file_util::get_file_path({dep}));
+    if (std::filesystem::exists(dep_path)) {
+      auto dep_time = std::filesystem::last_write_time(dep_path);
+      if (dep_time > newest_input) {
+        newest_input = dep_time;
+      }
+    } else {
+      return true;  // don't have a dep.
+    }
+  }
+
+  for (auto& out : task.output) {
+    auto out_path = std::filesystem::path(file_util::get_file_path({out}));
+    if (std::filesystem::exists(out_path)) {
+      auto out_time = std::filesystem::last_write_time(out_path);
+      if (out_time < newest_input) {
+        return true;
+      }
+    } else {
+      return true;  // don't have a dep.
+    }
+  }
+
+  return false;
+}