Windows support

[giann]

Make it work on Windows:

• build MIR for windows
• does pcre for windows?
• io and fs apis are somewhat different for windows

[giann]

Progress:

• [x] Compiling
• [x] PCRE: built in build.zig
• [x] Mimalloc: built in build.zig
• [x] MIR: built with build.zig but fails at runtime

[ghost]

if it helps the Go standard library is pretty readable:

https://github.com/golang/go/blob/go1.20.6/src/os/file_windows.go