Update smallvec and new_debug_unreachable

[taiki-e]

This removes two unmaintained dependencies (see servo/rust-smallvec#140 and crossbeam-rs/crossbeam#312 (comment)).

[rust-highfive]

The job x86_64-gnu-llvm-6.0 of your PR failed on Travis (raw log). Through arcane magic we have determined that the following fragments from the build log may contain information about the problem.

Click to expand the log.

travis_time:end:34dacb3a:start=1551256837683291170,finish=1551256838556473904,duration=873182734
$ git checkout -qf FETCH_HEAD
travis_fold:end:git.checkout

Encrypted environment variables have been removed for security reasons.
See https://docs.travis-ci.com/user/pull-requests/#pull-requests-and-security-restrictions
$ export SCCACHE_BUCKET=rust-lang-ci-sccache2
$ export SCCACHE_REGION=us-west-1
Setting environment variables from .travis.yml
$ export IMAGE=x86_64-gnu-llvm-6.0
---
[00:27:22]    |
[00:27:22] 71 | #[allow_internal_unstable]
[00:27:22]    | ^^^^^^^^^^^^^^^^^^^^^^^^^^
[00:27:22] 
[00:27:31] error: internal compiler error: src/librustc/ty/relate.rs:703: impossible case reached: can't relate: '_#0r with Type(RustaceansAreAwesome)
[00:27:31] thread 'rustc' panicked at 'Box<Any>', src/librustc_errors/lib.rs:620:9
[00:27:31] note: Run with `RUST_BACKTRACE=1` environment variable to display a backtrace.
[00:27:31] error: aborting due to previous error
[00:27:31] 
[00:27:31] 
[00:27:31] 
[00:27:31] note: the compiler unexpectedly panicked. this is a bug.
[00:27:31] 
[00:27:31] note: we would appreciate a bug report: https://github.com/rust-lang/rust/blob/master/CONTRIBUTING.md#bug-reports
[00:27:31] 
[00:27:31] note: rustc 1.34.0-dev running on x86_64-unknown-linux-gnu
[00:27:31] 
[00:27:31] note: compiler flags: -Z force-unstable-if-unmarked -C prefer-dynamic -C opt-level=2 -C prefer-dynamic -C debug-assertions=y -C link-args=-Wl,-rpath,$ORIGIN/../lib --crate-type dylib
[00:27:31] note: some of the compiler flags provided by cargo are hidden
[00:27:31] 
[00:27:31] error: Could not compile `rustc`.
[00:27:31] warning: build failed, waiting for other jobs to finish...

I'm a bot! I can only do what humans tell me to, so if this was not helpful or you have suggestions for improvements, please ping or otherwise contact @TimNN. (Feature Requests)

[Centril]

r? @kennytm

[kennytm]

😕 Failed to build stage1-rustc.

[00:27:31] error: internal compiler error: src/librustc/ty/relate.rs:703: impossible case reached: can't relate: '_#0r with Type(RustaceansAreAwesome)

[taiki-e]

@kennytm
Here is a full dump with backtrace: https://gist.github.com/taiki-e/cd1427d5e30ff8608a08267daa621446

The problem seems to be occurring here:

  14: <rustc::ty::subst::Kind<'tcx> as rustc::ty::relate::Relate<'tcx>>::relate

[taiki-e]

It seems to be the same ICE: #56440 (comment)

[kennytm]

Thanks. cc @bluss

[bors]

☔ The latest upstream changes (presumably #56946) made this pull request unmergeable. Please resolve the merge conflicts.

[Dylan-DPC-zz]

ping from triage @taiki-e is this blocked on that PR? since the PR got closed due to inactivity

[taiki-e]

This PR is blocked by the ICE in stage1 (that (closed) PR was also blocked by the same ICE), but I don't have time to look this, so I close this PR.