And introduce two new directives for ui tests:
* `run-crash`
* `run-fail-or-crash`
Normally a `run-fail` ui test like tests that panic shall not be
terminated by a signal like `SIGABRT`. So begin having that as a hard
requirement.
Some of our current tests do terminate by a signal/crash however.
Introduce and use `run-crash` for those tests. Note that Windows crashes
are not handled by signals but by certain high bits set on the process
exit code. Example exit code for crash on Windows: `0xc000001d`.
Because of this, we define "crash" on all platforms as "not exit with
success and not exit with a regular failure code in the range 1..=127".
Some tests behave differently on different targets:
* Targets without unwind support will abort (crash) instead of exit with
failure code 101 after panicking. As a special case, allow crashes for
`run-fail` tests for such targets.
* Different sanitizer implementations handle detected memory problems
differently. Some abort (crash) the process while others exit with
failure code 1. Introduce and use `run-fail-or-crash` for such tests.
This has now been approved as a language feature and no longer needs
a `rustc_` prefix.
Also change the `contracts` feature to be marked as incomplete and
`contracts_internals` as internal.
The extended syntax for function signature that includes contract clauses
should never be user exposed versus the interface we want to ship
externally eventually.
