我如何告诉CGO不要编译文件？

for a regular go file I say

// +build !windows

however cgo interprets this as c code to get compiled

So what do I have to do?

The build constraint must appear before your package declaration.

Incorrect

package mypackage

// +build !windows

// #include <header.h>
//
// ...
import "C"

Correct

// +build !windows

package mypackage

// #include <header.h>
//
// ...
import "C"