gen: clean up code generation

[tmc]

Operating System

• Windows
• macOS
• Linux
• FreeBSD
• Android
• iOS

What feature would you like to be added?

Currently gen.go cals "wincallbacks.go" which generates more than windows callsbacks.

suggestion: move code generation into some internal package and clean it up.

Why is this needed?

No response

[hajimehoshi]

You mean wincallback.go? This is originally from the Go repository https://cs.opensource.google/go/go/+/master:src/runtime/wincallback.go and we keep the same file/directory structure on purpose.