feat(WIN32): make it at least compilable

[vulptex]

I am really sorry for such a bad PR, shame on me. At least it makes it usable for people with MinGW-w64.

Could be used as a starting point for someone to-do a 'proper' port for Windows, if needed:

• [ ] fetch progname (easy one)
• [ ] stack traces for Windows
• [ ] addr2line for Windows