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rustc: Don't allocate a cnum to syntax crates

Syntax-only crates are no longer registered with the cstore, so there's no need
to allocate crate numbers to them. This ends up leaving gaps in the crate
numbering scheme which is not expected in the rest of the compiler.

Closes #13560
Give reduction-type tests in Bitv more natural names
parallelisation of shootout-k-nucleotide
Simplify implementation of Bitv::{all,none} using iter builtins.
syntax: Parses `&&` as `& &` whenever appropriate.

Closes #11227.
Guard variance inference for params bound in non-variance context.

Before adding a variance constrant for a given early-bound param,
check if it was meant to be inferred.

To support the above, added `fn is_to_be_inferred` to
`variance::ConstraintContext`.
Extended `syntax::{fold, ast_map}` to include lifetimes.

Part of this required added an override of `fold_type_method` in the
Folder for Ctx impl; it follows the same pattern as `fold_method`.

Also, as a drive-by fix, I moved all of the calls to `folder.new_id`
in syntax::fold's no-op default traversal to really be the first
statement in each function.

  * This is to uphold the invariant that `folder.new_id` is always
    called first (an unfortunate requirement of the current `ast_map`
    code), an invariant that we seemingly were breaking in e.g. the
    previous `noop_fold_block`.

  * Now it should be easier to see when adding new code that this
    invariant must be upheld.

  * (note that the breakage in `noop_fold_block` may not have mattered
    so much previously, since the only thing that blocks can bind are
    lifetimes, which I am only adding support for now.)
Drive-by: `pprust::*_to_str` for TypeMethod, Method, and FnDecl.
Regression test.
Add #[deriving(Hash)] to Result.
Tests for issue 5997 failure and success conditions.

Closes #5997.
Add span to error for missing type params on enums.
Change error for out of scope type params to be more helpful.
Catch forward declarations in default type params at AST conversion.
mk/tests.mk: Fix a typo causing make to give compiletest the wrong rt build dir (target instead of host).
Upgrade LLVM

This comes with a number of fixes to be compatible with upstream LLVM:

* Previously all monomorphizations of "mem::size_of()" would receive the same
  symbol. In the past LLVM would silently rename duplicated symbols, but it
  appears to now be dropping the duplicate symbols and functions now. The symbol
  names of monomorphized functions are now no longer solely based on the type of
  the function, but rather the type and the unique hash for the
  monomorphization.

* Split stacks are no longer a global feature controlled by a flag in LLVM.
  Instead, they are opt-in on a per-function basis through a function attribute.
  The rust #[no_split_stack] attribute will disable this, otherwise all
  functions have #[split_stack] attached to them.

* The compare and swap instruction now takes two atomic orderings, one for the
  successful case and one for the failure case. LLVM internally has an
  implementation of calculating the appropriate failure ordering given a
  particular success ordering (previously only a success ordering was
  specified), and I copied that into the intrinsic translation so the failure
  ordering isn't supplied on a source level for now.

* Minor tweaks to LLVM's API in terms of debuginfo, naming, c++11 conventions,
  etc.
configure: Enable libc++ with LLVM with clang

When clang is enabled, also pass through --enable-libcpp to LLVM's configure
command line to help it pick up the most recent c++ runtime library. This also
changes the mklldeps.py script to pick up on whether LLVM was linked against
stdc++ or c++ based on the --cxxflags that llvm-config prints.

In an ongoing attempt to update LLVM, the bots need to update their C compilers
to something that supports c++11 (LLVM recently switched). The OSX bots are
running Lion (10.7), which only supports up to gcc 4.2 and clang 3.2. Apparently
the libstdc++ is too old (even on the most updated command line tools) for LLVM,
but using libc++ instead appears to work just fine.
configure: Enable clang for older OSX gcc versions

OSX often has a more recent version of clang than it does for GCC. When an older
version of gcc is detected on OSX, the --enable-clang flag is implicitly
enabled.
etc: The --system-libs flag is LLVM 3.5+

Older version of LLVM did not have this flag, so we need to fall back to our
previous library detection when using older versions of LLVM.