MSVC 2022 cannot build this project

Using MSVC 2022 Community Edition:

```
PS  D:\temp\cmark-gfm> nmake

Microsoft (R) Program Maintenance Utility Version 14.38.33134.0
Copyright (C) Microsoft Corporation.  All rights reserved.

makefile(4) : fatal error U1001: syntax error : illegal character '?' in macro
Stop.
```