Update to 1.24.0

* Disable SunOS support for a while

Changelog:
Version 1.24.0 (2018-02-15)
Language
    External sysv64 ffi is now available. eg. extern "sysv64" fn foo () {}

Compiler
    rustc now uses 16 codegen units by default for release builds. For
      the fastest builds, utilize codegen-units=1.
    Added armv4t-unknown-linux-gnueabi target.
    Add aarch64-unknown-openbsd support

Libraries
    str::find::<char> now uses memchr. This should lead to a 10x improvement
      in performance in the majority of cases.
    OsStr's Debug implementation is now lossless and consistent with Windows.
    time::{SystemTime, Instant} now implement Hash.
    impl From<bool> for AtomicBool
    impl From<{CString, &CStr}> for {Arc<CStr>, Rc<CStr>}
    impl From<{OsString, &OsStr}> for {Arc<OsStr>, Rc<OsStr>}
    impl From<{PathBuf, &Path}> for {Arc<Path>, Rc<Path>}
    float::from_bits now just uses transmute. This provides some optimisations
      from LLVM.
    Copied AsciiExt methods onto char
    Remove T: Sized requirement on ptr::is_null()
    impl From<RecvError> for {TryRecvError, RecvTimeoutError}
    Optimised f32::{min, max} to generate more efficent x86 assembly
    [u8]::contains now uses memchr which provides a 3x speed improvement

Stabilized APIs
    RefCell::replace
    RefCell::swap
    atomic::spin_loop_hint

The following functions can now be used in a constant expression.
eg. let buffer: [u8; size_of::<usize>()];, static COUNTER: AtomicUsize =
AtomicUsize::new(1);

    AtomicBool::new
    AtomicUsize::new
    AtomicIsize::new
    AtomicPtr::new
    Cell::new
    {integer}::min_value
    {integer}::max_value
    mem::size_of
    mem::align_of
    ptr::null
    ptr::null_mut
    RefCell::new
    UnsafeCell::new

Cargo
    Added a workspace.default-members config that overrides implied --all
      in virtual workspaces.
    Enable incremental by default on development builds. Also added
      configuration keys to Cargo.toml and .cargo/config to disable on
      a per-project or global basis respectively.

Misc
Compatibility Notes
    Floating point types Debug impl now always prints a decimal point.
    Ipv6Addr now rejects superfluous ::'s in IPv6 addresses This is in
      accordance with IETF RFC 4291 Sec. 2.2.
    Unwinding will no longer go past FFI boundaries, and will instead abort.
    Formatter::flags method is now deprecated. The sign_plus, sign_minus,
      alternate, and sign_aware_zero_pad should be used instead.
    Leading zeros in tuple struct members is now an error
    column!() macro is one-based instead of zero-based
    fmt::Arguments can no longer be shared across threads
    Access to #[repr(packed)] struct fields is now unsafe
    Cargo sets a different working directory for the compiler

(ryoon)