Add spacing between trait functions

Fixes #42988.

<img width="1440" alt="screen shot 2017-07-09 at 17 02 16" src="https://user-images.githubusercontent.com/3050060/27995068-672a3208-64c8-11e7-9bc7-c7288f2cd27b.png">

Fix stage 2 builds with a custom libdir.

When copying libstd for the stage 2 compiler, the builder ignores the
configured libdir/libdir_relative configuration parameters.  This causes
the compiler to fail to find libstd, which cause any tools built with the
stage 2 compiler to fail.

To fix this, make the copy steps of rustbuild aware of the libdir_relative
parameter when the stage >= 2.  Also update the dist target to be aware of
the new location of libstd.

Redox: Fix Condvar.wait(); do not lock mutex twice

The atomic_xchg() loop locks the mutex, so the call to mutex_lock is
incorrect, and blocks.

Implemented `TypeFoldable` for `TypeError`s.

This is quite handy in some user code, for instance to pull out type errors from an inference context when `fresh_substs_for_item` has been used before.

Raise alignment limit from 2^15 to 2^31 - 1

Fixes #42960

Fix links for typeck diagnostics without tripping tidy

Pick up #42624 to fix #43070 (cc @frewsxcv). I fixed a few other links while I was at it.

Remove unused code from librustc_errors

While extracting librustc_errors into a [reusable library](https://github.com/kevinmehall/codemap-diagnostic), I noticed some obsolete code that the `dead_code` warning missed because it was marked `pub` but not used elsewhere.

Fold E0612, E0613 into E0609

As discussed in #42945, with PR 1506 tuple indices are no longer considered a separate case from normal field. This PR folds E06012 ("tuple index out of bounds") and E0613 ("type is not a tuple") into E0609 ("type does not have field with that name")

Resolves #42945

Fix Rustbuild linking on Illumos

Illumos (an OpenSolaris fork) expects to get several extra library references for some system functions used by Rust standard library. This commit adds required linker options to rustbuild, which is currently doesn't work on Illumos-based operating systems.

Implement O(1)-time Iterator::nth for Range*, and slim the Step trait

Fixes #43064.
Fixes part of #39975.
Fixes items 1 <s>and 3</s> of #42168.
CC #27741.

I think #42310 and #43012 should not have landed without the `nth` part of this PR, but oh well.

Skip the main thread's manual stack guard on Linux

Linux doesn't allocate the whole stack right away, and the kernel has its own stack-guard mechanism to fault when growing too close to an existing mapping.  If we map our own guard, then the kernel starts enforcing a rather large gap above that, rendering much of the possible stack space useless.

Instead, we'll just note where we expect rlimit to start faulting, so our handler can report "stack overflow", and trust that the kernel's own stack guard will work.

Fixes #43052.
r? @alexcrichton

### Kernel compatibility:

Strictly speaking, Rust claims support for Linux kernels >= 2.6.18, and stack guards were only added to mainline in 2.6.36 for [CVE-2010-2240].  But since that vulnerability was so severe, the guards were backported to many stable branches, and Red Hat patched this all the way back to RHEL3's 2.4.21!  I think it's reasonable for us to assume that any *supportable* kernel should have these stack guards.

At that time, the kernel only enforced one page of padding between the stack and other mappings, but thanks to [Stack Clash] that padding is now much larger, causing #43052.  The kernel side of those fixes are in [CVE-2017-1000364], which Red Hat has backported to at least RHEL5's 2.6.18 so far.

[CVE-2010-2240]: https://access.redhat.com/security/cve/CVE-2010-2240
[CVE-2017-1000364]: https://access.redhat.com/security/cve/CVE-2017-1000364
[Stack Clash]: https://access.redhat.com/security/vulnerabilities/stackguard

When copying libstd for the stage 2 compiler, the builder ignores the
configured libdir/libdir_relative configuration parameters.  This causes
the compiler to fail to find libstd, which cause any tools built with the
stage 2 compiler to fail.

To fix this, make the copy steps of rustbuild aware of the libdir_relative
parameter when the stage >= 2.  Also update the dist target to be aware of
the new location of libstd.

Make sufficiently old or low-impact compatibility lints deny-by-default

Needs crater run before proceeding.

r? @nikomatsakis

Fix some tests on Linux

This is going to be a hard error while all private-in-public errors from rustc_privacy will be reclassified into lints.

Replace the global fulfillment cache with the evaluation cache

This uses the new "Chalk" ParamEnv refactoring to check "global" predicates in an empty environment, which should be correct because global predicates aren't affected by a consistent environment.

Fixes #39970.
Fixes #42796.

r? @nikomatsakis

Resolves #42945

remove associated_consts feature gate

Currently struggling to run tests locally (something about jemalloc target missing).

cc #29646

This helps avoid cache pollution. Also add more comments explaining
that.

The evaluation cache already exists, and it can handle differing
parameter environments natively.

Fixes #39970.
Fixes #42796.

This is just duplicating the logic from the old fulfillment cache, so
I'm not sure it is 100% correct, but it should not be more wrong than
the old logic.

Previously, coinductive matching was only blocked on the fulfillment
path, and ignored on the evaluation path.

Linux doesn't allocate the whole stack right away, and the kernel has
its own stack-guard mechanism to fault when growing too close to an
existing mapping.  If we map our own guard, then the kernel starts
enforcing a rather large gap above that, rendering much of the possible
stack space useless.

Instead, we'll just note where we expect rlimit to start faulting, so
our handler can report "stack overflow", and trust that the kernel's own
stack guard will work.

Fixes #43052.

The atomic_xchg() loop locks the mutex, so the call to mutex_lock is
incorrect, and blocks.