src: Fix windows build flag
src: Fix windows build flag

https://github.com/nwjs/chromium.src/commit/0ef51d3a5a383f962a7bf59aba6eaba0f65d7881

nwjs/nw.js,nwjs/nw.js,nwjs/nw.js,nwjs/nw.js,nwjs/nw.js,nwjs/nw.js