Per [RFC 579](https://github.com/rust-lang/rfcs/pull/579), this commit
adds a new `std::process` module. This module is largely based on the
existing `std::old_io::process` module, but refactors the API to use
`OsStr` and other new standards set out by IO reform.

The existing module is not yet deprecated, to allow for the new API to
get a bit of testing before a mass migration to it.

This resolves a number of bugs that trigger stack overflows or other cyclic errors.

r? @nick29581 (it is based on work that you started)
f? @jroesch (also based on your branch)

and the type appearing in the trait would (previously) trigger an
error message. The code is now accepted. No reported issue that I am
aware of.

fetch trait definitions. This allows is to be used early in the compiler
without triggering ICEs. Also make -Z verbose less horrifyingly ugly.

predicates and renaming some things.

and predicates. Try to document how things work. More cleanup is
needed here but I had to draw the line somewhere gosh darn it.

Split the predicates listing out of `TraitDef` and `TypeScheme` and into a separate map, `tcx.predicates`, that is used for both traits and other kinds of items. Also use two newtypes to distinguish
instantiated predicates from the raw, unsubstituted predicates extracted from the map.

There are two dots at the end of a line in the documentation of std::char.

PR #22012 followup: clean up vtable::check_object_cast by reusing `fresh_ty`

(hat tip to nikomatsakis, who was the one who pointed out this simplification to the logic.)

This flag seems to have erroneously been set to `true`.

(hat tip to nikomatsakis who was the one who pointed out this
simplification to the logic.)

- DoubleEndedIterator
- ExactSizeIterator
- RandomAccessIterator

This commit is an implementation of [RFC 807][rfc] which adds a `std::net`
module for basic neworking based on top of `std::io`. This module serves as a
replacement for the `std::old_io::net` module and networking primitives in
`old_io`.

[rfc]: fillmein

The major focus of this redesign is to cut back on the level of abstraction to
the point that each of the networking types is just a bare socket. To this end
functionality such as timeouts and cloning has been removed (although cloning
can be done through `duplicate`, it may just yield an error).

With this `net` module comes a new implementation of `SocketAddr` and `IpAddr`.
This work is entirely based on #20785 and the only changes were to alter the
in-memory representation to match the `libc`-expected variants and to move from
public fields to accessors.

This commit is an implementation of [RFC 807][rfc] which adds a `std::net`
module for basic neworking based on top of `std::io`. This module serves as a
replacement for the `std::old_io::net` module and networking primitives in
`old_io`.

[rfc]: fillmein

The major focus of this redesign is to cut back on the level of abstraction to
the point that each of the networking types is just a bare socket. To this end
functionality such as timeouts and cloning has been removed (although cloning
can be done through `duplicate`, it may just yield an error).

With this `net` module comes a new implementation of `SocketAddr` and `IpAddr`.
This work is entirely based on #20785 and the only changes were to alter the
in-memory representation to match the `libc`-expected variants and to move from
public fields to accessors.

- DoubleEndedIterator
- ExactSizeIterator
- RandomAccessIterator

Conflicts:
	src/libsyntax/feature_gate.rs

This commit tweaks the interface of the `std::env` module to make it more
ergonomic for common usage:

* `env::var` was renamed to `env::var_os`
* `env::var_string` was renamed to `env::var`
* `env::args` was renamed to `env::args_os`
* `env::args` was re-added as a panicking iterator over string values
* `env::vars` was renamed to `env::vars_os`
* `env::vars` was re-added as a panicking iterator over string values.

This should make common usage (e.g. unicode values everywhere) more ergonomic
as well as "the default". This is also a breaking change due to the differences
of what's yielded from each of these functions, but migration should be fairly
easy as the defaults operate over `String` which is a common type to use.

[breaking-change]

Fixes issue #22174.

When projecting associate types for a trait's default methods, the
trait itself was added to the predicate candidate list twice: one from
parameter environment, the other from trait definition. Then the
duplicates were deemed as code ambiguity and the compiler rejected the
code. Simply checking and dropping the duplicates solves the issue.

Closes #22036

This resulted in some very unexpected fallout such as empty llvm-ir, llvm-bc and asm in some cases.
See #22183 for related info.

r? @alexcrichton

OpenBSD doesn't have thread-local-storage support (yet).
Permit to compile (and run) `check-stage1-crates` under OpenBSD.

Fixes #21062.

It doesn't have to be a literal memory allocation (ala malloc), e.g. it
can be in static memory, so saying "allocated" is mildly misleading.

Thanks to @mahkoh for pointing it out.

r? @steveklabnik

It returns `false`, not `None`.

Given that this is entirely internal, this enhancement isn't going to be needed. And if it is, we'll add it.

Closes #2741.

r? @alexcrichton