rust/tests/crashes

This is serves as a collection of crashes so that accidental ICE fixes are tracked. This was formally done at https://github.com/rust-lang/glacier but doing it inside the rustc testsuite is more convenient.

It is imperative that a test in the suite causes an internal compiler error/panic or makes rustc crash in some other way. Accepted exit codes are: 101 (may be expanded later)

When adding crashes from https://github.com/rust-lang/rust/issues, the issue number should be noted in the file name (12345.rs should suffice) and perhaps also inside the file via //@ known-bug #4321

If you happen to fix one of the crashes, please move it to tests/ui! :)