Provide a way of learning if the platform is unsupported

[From rust's std](https://github.com/rust-lang/rust/blob/864bdf7843e1ceabc824ed86d97006acad6af643/library/std/src/backtrace.rs#L344-L346):

> If no frames came out assume that this is an unsupported platform since `backtrace` doesn't provide a way of learning this right now

This seems like a reasonable feature request?