rustc: Always mark #[crate_name] as used

It's just an annoying error if you use --crate-name on the command line and you
also have a #[crate_name] specified
rustc: Exclude #[repr(C)] from non camel case

C structs predominately do not use camel case identifiers, and we have a clear
indicator for what's a C struct now, so excuse all of them from this stylistic
lint.
rustdoc: render 1-tuples as (T,) instead of (T)
mark std::hash experimental

The `hash` module was not included in an earlier pass that sets baseline
stability of modules within `std` to `experimental`.
Fix spans for attributes

They used to be one token too long, so you'd see things like
```
rust/rust/test.rs:1:1: 2:2 warning: unused attribute,
rust/rust/test.rs:1 #![foo]
rust/rust/test.rs:2 #![bar]
```
instead of
```
test.rs:1:1: 1:8 warning: unused attribute, #[warn(unused_attribute)] on
by default
test.rs:1 #![foo]
          ^~~~~~~
```
libc: Switch open to use a mode_t on unix

While I'm at it, export O_SYNC with the other flags that are exported.

Closes #15582
auto merge of #15617 : aturon/rust/std-more-experimental, r=alexcrichton

The `hash` module was not included in an earlier pass that sets baseline
stability of modules within `std` to `experimental`.
Fix Documentation Typo in libstd
auto merge of #15614 : lucidd/rust/#15474, r=alexcrichton

This fixes #15474
auto merge of #15621 : sfackler/rust/attr-span, r=cmr

They used to be one token too long, so you'd see things like
```
rust/rust/test.rs:1:1: 2:2 warning: unused attribute,
rust/rust/test.rs:1 #![foo]
rust/rust/test.rs:2 #![bar]
```
instead of
```
test.rs:1:1: 1:8 warning: unused attribute, #[warn(unused_attribute)] on
by default
test.rs:1 #![foo]
          ^~~~~~~
```
Use a nicer Show impl for Name
auto merge of #15584 : alexcrichton/rust/warn-annoyances, r=cmr

* Don't warn about `#[crate_name]` if `--crate-name` is specified
* Don't warn about non camel case identifiers on `#[repr(C)]` structs
* Switch `mode` to `mode_t` in libc.
Implement Hash trait for TreeSet and TreeMap.
auto merge of #15633 : nham/rust/hash_treeset, r=alexcrichton

cc #15294
auto merge of #15639 : supr/rust/master, r=sfackler

* Fixes a typo in the libstd documentation, referring UPD instead of UDP
Add an iterate function to core::iter

Implementation by Kevin Ballard.

The function returns an Unfold iterator producing an infinite stream
of results of repeated applications of the function, starting from
the provided seed value.
auto merge of #15507 : jakub-/rust/iterate, r=alexcrichton

The new iterator takes a function and produces an infinite stream
of results of repeated applications of the function, starting from
the provided seed value.
auto merge of #15646 : jbclements/rust/method-macros, r=cmr

This patch adds support for macros in method position. It follows roughly the template for Item macros, where an outer `Method` wrapper contains a `Method_` enum which can either be a macro invocation or a standard macro definition. 

One note; adding support for macros that expand into multiple methods is not included here, but should be a simple parser change, since this patch updates the type of fold_macro to return a smallvector of methods.

For reviewers, please pay special attention to the parser changes; these are the ones I'm most concerned about.

Because of the small change to the interface of fold_method, this is a ...

[breaking change]