[goalc] add a build system (#704)

* add first attempt at build system

* fix stupid bug

* try again

goalc/main.cpp

@@ -48,7 +48,7 @@ int main(int argc, char** argv) {
   // Init REPL
   // the compiler may throw an exception if it fails to load its standard library.
   try {
-    std::unique_ptr<Compiler> compiler = std::make_unique<Compiler>();
+    std::unique_ptr<Compiler> compiler;
     if (argument.empty()) {
       ReplStatus status = ReplStatus::WANT_RELOAD;
       while (status == ReplStatus::WANT_RELOAD) {
@@ -59,6 +59,7 @@ int main(int argc, char** argv) {
         }
       }
     } else {
+      compiler = std::make_unique<Compiler>();
       compiler->run_front_end_on_string(argument);
     }
   } catch (std::exception& e) {