panic = "abort" on release

[jon-chuang]

This can reduce binary size and improve instr cache performance. So maybe we should test this.

[daira]

It's also completely necessary for security and correctness in mixed-language projects, because panics across an FFI boundary are undefined behaviour. By their nature it's impossible to prevent panics, and the only other alternative is to add a bunch of verbose and error-prone boilerplate to all code that crosses an FFI boundary — including in libraries you don't want to have to change. See also zcash/librustzcash#78 and rust-lang/rust#52652, in particular my comment here and the subsequent discussion.

Note that panic = "abort" only takes effect for a top-level crate, not dependencies.