Change important printfs to lg::print (#3355)

This allows them to be logged into a file, useful for debugging.

With this, GOAL `format` and C-kernel `Msg` (and its variants) will be
logged.

common/log/log.cpp

@@ -112,8 +112,31 @@ void log_print(const char* message) {
     }
   }
 }
+
+void log_vprintf(const char* format, va_list arg_list) {
+  {
+    // We always immediately flush prints because since it has no associated level
+    // it could be anything from a fatal error to a useless debug log.
+    std::lock_guard<std::mutex> lock(gLogger.mutex);
+    if (gLogger.fp) {
+      // Log to File
+      vfprintf(gLogger.fp, format, arg_list);
+      fflush(gLogger.fp);
+    }
+
+    if (gLogger.stdout_log_level < lg::level::off_unless_die) {
+      vprintf(format, arg_list);
+      fflush(stdout);
+      fflush(stderr);
+    }
+  }
+}
 }  // namespace internal
 
+void printstd(const std::string& format, va_list arg_list) {
+  internal::log_vprintf(format.c_str(), arg_list);
+}
+
 // how many extra log files for a single program should be kept?
 constexpr int LOG_ROTATE_MAX = 10;