Also modifies the generation script to emit 2018 edition paths.

…er discussion rust-lang#50264

It is broken and unused

The bugs that this was working around have been fixed in LLVM 9.

Some fixes for i686-msvc and Windows have landed on the `backtrace`
crate but hadn't made their way here yet. Let's update that and see if
it passes CI.

Unfortunately due to an Azure quirk the TOOLSTATE_REPO_ACCESS_TOKEN is
not suitable to gate whether to push new commits to the repo, as if it's
not defined on the Azure side it will actually be set to the literal
`$(TOOLSTATE_REPO_ACCESS_TOKEN)`, which screws everything up.

This instead adds another, non-secret environment variable to gate
publishing: TOOLSTATE_PUBLISH. As non-secret environment variables
behave correctly this fixes the issue.

allow clippy::unreadable_literal in unicode tables

Also modifies the generation script to emit 2018 edition paths.

Introduce `as_deref` to Option

This is re-submission for rust-lang#59628.
Renames `deref()` to `as_deref()` and adds `deref_mut()` impls and tests.

CC rust-lang#50264

r? @Kimundi
(I picked you as you're the previous reviewer.)

rustc: precompute the largest Niche and store it in LayoutDetails.

Since we only ever can use at most one niche, it makes sense to just store that in the layout, for the simplest caching (especially as it's almost trivial to compute).

There might be a speedup from this, but even if it's marginal now, the caching would be a more significant benefit for future optimization attempts.

…lexcrichton

Remove support for -Zlower-128bit-ops

It is broken and unused

cc rust-lang#58969

blocked rust-lang/compiler-builtins#302 (removes definitions of the lang items removed in this PR)

r? @alexcrichton

Remove vector fadd/fmul reduction workarounds

The bugs that this was working around have been fixed in LLVM 9.

r? @gnzlbg

code cleanup

remove all codes that are not used by vxWorks

…=pietroalbini

Attempt to fix backtrace tests on i686-msvc

Some fixes for i686-msvc and Windows have landed on the `backtrace`
crate but hadn't made their way here yet. Let's update that and see if
it passes CI.

Disable d32 on armv6 hf targets

We already do this on armv7 targets. It seems that this now gets enabled by default if '+vfp2` is specified, so disable it explicitly.

Hopefully fixes rust-lang#62841.

r? @alexcrichton

Initialize the MSP430 AsmParser

Hopefully fixes rust-lang#59077.

r? @alexcrichton

…lexcrichton

ci: gate toolstate repo pushes on the TOOLSTATE_PUBLISH envvar

This PR fixes toolstate failing to push on the LinuxTools PR builder by gating the pushes on the new `TOOLSTATE_PUBLISH` environment variable, which is set on prod credentials but not on the PR ones. The old code checked whether the access token was set, but that doesn't work due to an Azure quirk.

For a bit of background, secret environment variables are not available by default, but each step needs to explicitly declare which secret vars to load:

```yaml
- bash: echo foo
  env:
    SECRET_VAR: $(SECRET_VAR)
```

This works fine when the variable is present but when it's missing, instead of setting `SECRET_VAR` to an empty string or just not setting it at all, Azure Pipelines puts the literal `$(SECRET_VAR)` as the content, which completly breaks the old check we had. I tried almost every thing to make this work in a sensible way, and the only conclusion I reached is to set the variable at the top level with the runtime expression evaluation syntax, which sets the variable to an empty string if missing:

```yaml
# At the top:
variables:
  - name: MAYBE_SECRET_VAR
    value: $[ variables.MAYBE_SECRET_VAR ]

# In the step:
- bash: echo foo
  env:
    SECRET_VAR: $(MAYBE_SECRET_VAR)
```

While that *could've worked* it was ugly and messy, so I just opted to add yet another non-secret variable.

r? @alexcrichton
fixes rust-lang#62811