rustc: Switch tuple structs to have private fields

This is a continuation of the work done in #13184 to make struct fields private
by default. This commit finishes RFC 4 by making all tuple structs have private
fields by default. Note that enum variants are not affected.

A tuple struct having a private field means that it cannot be matched on in a
pattern match (both refutable and irrefutable), and it also cannot have a value
specified to be constructed. Similarly to private fields, switching the type of
a private field in a tuple struct should be able to be done in a backwards
compatible way.

The one snag that I ran into which wasn't mentioned in the RFC is that this
commit also forbids taking the value of a tuple struct constructor. For example,
this code now fails to compile:

    mod a {
        pub struct A(int);
    }

    let a: fn(int) -> a::A = a::A; //~ ERROR: first field is private

Although no fields are bound in this example, it exposes implementation details
through the type itself. For this reason, taking the value of a struct
constructor with private fields is forbidden (outside the containing module).

RFC: 0004-private-fields
Switch some tuple structs to pub fields

This commit deals with the fallout of the previous change by making tuples
structs have public fields where necessary (now that the fields are private by
default).
rustc: Stop using LLVMGetSectionName

The recent pull request to remove libc from libstd has hit a wall in compiling
on windows, and I've been trying to investigate on the try bots as to why (it
compiles locally just fine). To the best of my knowledge, the LLVM section
iterator is behaving badly when iterating over the sections of the libc DLL.

Upon investigating the LLVMGetSectionName function in LLVM, I discovered that
this function doesn't always return a null-terminated string. It returns the
data pointer of a StringRef instance (LLVM's equivalent of &str essentially),
but it has no method of returning the length of the name of the section.

This commit modifies the section iteration when loading libraries to invoke a
custom LLVMRustGetSectionName which will correctly return both the length and
the data pointer.

I have not yet verified that this will fix landing liblibc, as it will require a
snapshot before doing a full test. Regardless, this is a worrisome situation
regarding the LLVM API, and should likely be fixed anyway.
rustllvm: Remove a no longer needed file

The .def.in files haven't been necessary since the switch to static linking
awhile back.
std: override clone_from for Vec.

A vector can reuse its allocation (and the allocations/resources of any
contained values) when cloning into an already-instantiated vector, so
we might as well do so.
serialize: add a few missing pubs to base64
compiletest: Fix bitrotted win32 routines
test/debug-info: Add/remove ignore-win32 flags

Fixes #10474
test/run-pass: Add/remove some ignore-win32 flags
Removed managed boxes from libarena.
`extern crate` and `mod` are not easily confused

Remove some statements that used to refer to similarities between `mod` and
`extern mod`, before the latter was renamed to `extern crate`.
Fix reference to "these two traits."

There are actually three traits listed.
Minor spelling/grammar/usage fixes.

Note: "different to" is not exactly incorrect, but "different from" is more
commonly accepted in both US and Commonwealth English, and also more
consistent with other usage within this tutorial.
fix Option<~ZeroSizeType>

1778b6361627c5894bf75ffecf427573af02d390 provided the guarantee of no
`exchange_free` calls for ~ZeroSizeType, so a sentinel can now be used
without overhead.

Closes #11998
Update emacs mode to support new `#![inner(attribute)]` syntax.
syntax: Remove AbiSet, use one Abi

This change removes the AbiSet from the AST, converting all usage to have just
one Abi value. The current scheme selects a relevant ABI given a list of ABIs
based on the target architecture and how relevant each ABI is to that
architecture.

Instead of this mildly complicated scheme, only one ABI will be allowed in abi
strings, and pseudo-abis will be created for special cases as necessary. For
example the "system" abi exists for stdcall on win32 and C on win64.

Closes #10049
std: Document builtin syntax extensions

These syntax extensions need a place to be documented, and this starts passing a
`--cfg dox` parameter to `rustdoc` when building and testing documentation in
order to document macros so that they have no effect on the compiled crate, but
only documentation.

Closes #5605
Bump version to 0.11-pre

This also changes some of the download links in the documentation
to 'nightly'.
Test fixes from the rollup
auto merge of #13290 : alexcrichton/rust/rollup, r=alexcrichton

Closes #13285 (rustc: Stop using LLVMGetSectionName)
Closes #13280 (std: override clone_from for Vec.)
Closes #13277 (serialize: add a few missing pubs to base64)
Closes #13275 (Add and remove some ignore-win32 flags)
Closes #13273 (Removed managed boxes from libarena.)
Closes #13270 (Minor copy-editing for the tutorial)
Closes #13267 (fix Option<~ZeroSizeType>)
Closes #13265 (Update emacs mode to support new `#![inner(attribute)]` syntax.)
Closes #13263 (syntax: Remove AbiSet, use one Abi)