read arguments from response file

[kloenk]

rustc supports reading arguments from a file, if you give them via @<filename>.

I would love to see this feature in bindgen

[emilio]

Yes, this would be useful. We have an ad-hoc thing in Firefox for this: https://searchfox.org/mozilla-central/rev/d25eb00ab4e90cc0130cd18f303a04cc2a2f8409/servo/components/style/build_gecko.rs#27-40