Fixes rust-lang#34798

LLVM 4.0 changes this. This change is fine to make for LLVM 3.9 as we
won't have alignments greater than 2^32-1.

And libcore/benches

cc rust-lang#39569 -- almost certainly a fix for that

* Moved algorithm explanation to module docs
* Added ``` before and after the examples
* Explanation of the `rbox`, `ibox` and `cbox` names
* Added docs about the breaking types to `Breaks`

This is much nicer for callers who want to short-circuit real I/O errors
with `?`, because they can write this

    if let Some(status) = foo.try_wait()? {
        ...
    } else {
        ...
    }

instead of this

    match foo.try_wait() {
        Ok(status) => {
            ...
        }
        Err(err) if err.kind() == io::ErrorKind::WouldBlock => {
            ...
        }
        Err(err) => return Err(err),
    }

The original design of `try_wait` was patterned after the `Read` and
`Write` traits, which support both blocking and non-blocking
implementations in a single API. But since `try_wait` is never blocking,
it makes sense to optimize for the non-blocking case.

Tracking issue: rust-lang#38903

It claims to accept most GNU linker options, but in fact most of them
have no effect and instead it requires some special options which are
easier to handle in a separate trait.

Currently added:
 - `export_symbols`: works on executables as special Emscripten case
since staticlibs/dylibs aren't compiled to JS, while exports are
required to be accessible from JS.
Fixes rust-lang#39171.
 - `optimize` - translates Rust's optimization level to Emscripten
optimization level (whether passed via `-C opt-level=...` or `-O...`).
Fixes rust-lang#36899.
 - `debuginfo` - translates debug info; Emscripten has 5 debug levels
while Rust has 3, so chose to translate `-C debuginfo=1` to `-g3`
(preserves whitespace, variable and function names for easy debugging).
Fixes rust-lang#36901.
 - `no_default_libraries` - tells Emscripten to exlude `memcpy` and co.

The current manifests encode this with a dash in the name, so we should preserve
that!

lint/ctypes: Don't warn on sized structs with PhantomData.

Fixes rust-lang#34798

Add Emscripten-specific linker

Emscripten claims to accept most GNU linker options, but in fact most of `-Wl,...` are useless for it and instead it requires some additional special options which are easier to handle in a separate trait.

Currently added:
 - `export_symbols`: works on executables as special Emscripten case since staticlibs/dylibs aren't compiled to JS, while exports are required to be accessible from JS.
Fixes rust-lang#39171.
 - `optimize` - translates Rust's optimization level to Emscripten optimization level (whether passed via `-C opt-level=...` or `-O...`).
Fixes rust-lang#36899.
 - `debuginfo` - translates debug info; Emscripten has 5 debug levels while Rust has 3, so chose to translate `-C debuginfo=1` to `-g3` (preserves whitespace, variable and function names for easy debugging).
Fixes rust-lang#36901.
 - `no_default_libraries` - tells Emscripten to exclude `memcpy` and co.

TODO (in future PR): dynamic linking via `SIDE_MODULE` / `MAIN_MODULE` mechanism.

make Child::try_wait return io::Result<Option<ExitStatus>>

This is much nicer for callers who want to short-circuit real I/O errors
with `?`, because they can write this

    if let Some(status) = foo.try_wait()? {
        ...
    } else {
        ...
    }

instead of this

    match foo.try_wait() {
        Ok(status) => {
            ...
        }
        Err(err) if err.kind() == io::ErrorKind::WouldBlock => {
            ...
        }
        Err(err) => return Err(err),
    }

The original design of `try_wait` was patterned after the `Read` and
`Write` traits, which support both blocking and non-blocking
implementations in a single API. But since `try_wait` is never blocking,
it makes sense to optimize for the non-blocking case.

Tracking issue: rust-lang#38903

…crichton

[LLVM 4.0] Use 32-bits for alignment

LLVM 4.0 changes this. This change is fine to make for LLVM 3.9 as we
won't have alignments greater than 2^32-1.

A few documentation improvements for `syntax::print::pp`

* Moved algorithm explanation to module docs
* Added ``` before and after the examples
* Explanation of the `rbox`, `ibox` and `cbox` names
* Added docs about the breaking types to `Breaks`

…lexcrichton

Extract collections benchmarks to libcollections/bench

Good suggestion from @stjepang rust-lang#39484 (comment)

r? @alexcrichton

… r=michaelwoerister

Handle the case where an intermediate node can't be recreated

This solution grows the graph, but this is quite the corner case.

r? @michaelwoerister

Bump stable release date

cc rust-lang#39623

Rename manifest_version to manifest-version

The current manifests encode this with a dash in the name, so we should preserve
that!