This commit is the result of the FCPs ending for the 1.8 release cycle for both
the libs and the lang suteams. The full list of changes are:

Stabilized

* `braced_empty_structs`
* `augmented_assignments`
* `str::encode_utf16` - renamed from `utf16_units`
* `str::EncodeUtf16` - renamed from `Utf16Units`
* `Ref::map`
* `RefMut::map`
* `ptr::drop_in_place`
* `time::Instant`
* `time::SystemTime`
* `{Instant,SystemTime}::now`
* `{Instant,SystemTime}::duration_since` - renamed from `duration_from_earlier`
* `{Instant,SystemTime}::elapsed`
* Various `Add`/`Sub` impls for `Time` and `SystemTime`
* `SystemTimeError`
* `SystemTimeError::duration`
* Various impls for `SystemTimeError`
* `UNIX_EPOCH`
* `ops::{Add,Sub,Mul,Div,Rem,BitAnd,BitOr,BitXor,Shl,Shr}Assign`

Deprecated

* Scoped TLS (the `scoped_thread_local!` macro)
* `Ref::filter_map`
* `RefMut::filter_map`
* `RwLockReadGuard::map`
* `RwLockWriteGuard::map`
* `Condvar::wait_timeout_with`

Closes #27714
Closes #27715
Closes #27746
Closes #27748
Closes #27908
Closes #29866

.copy_from_slice() does the same job of .clone_from_slice(), but the
former is explicitly for Copy elements and calls `memcpy` directly, and
thus is it efficient without optimization too.

These were added a long time ago but we long since switched the lint back to
allow-by-default, so these annotations shouldn't be necessary.

This commit implements the stabilization of the custom hasher support intended
for 1.7 but left out due to some last-minute questions that needed some
decisions. A summary of the actions done in this PR are:

Stable

* `std::hash::BuildHasher`
* `BuildHasher::Hasher`
* `BuildHasher::build_hasher`
* `std::hash::BuildHasherDefault`
* `HashMap::with_hasher`
* `HashMap::with_capacity_and_hasher`
* `HashSet::with_hasher`
* `HashSet::with_capacity_and_hasher`
* `std::collections::hash_map::RandomState`
* `RandomState::new`

Deprecated

* `std::collections::hash_state`
* `std::collections::hash_state::HashState` - this trait was also moved into
  `std::hash` with a reexport here to ensure that we can have a blanket impl to
  prevent immediate breakage on nightly. Note that this is unstable in both
  location.
* `HashMap::with_hash_state` - renamed
* `HashMap::with_capacity_and_hash_state` - renamed
* `HashSet::with_hash_state` - renamed
* `HashSet::with_capacity_and_hash_state` - renamed

Closes #27713

it is pre-RFC1214 junk

This commit removes the `-D warnings` flag being passed through the makefiles to
all crates to instead be a crate attribute. We want these attributes always
applied for all our standard builds, and this is more amenable to Cargo-based
builds as well.

Note that all `deny(warnings)` attributes are gated with a `cfg(stage0)`
attribute currently to match the same semantics we have today

This commit stabilizes and deprecates the FCP (final comment period) APIs for
the upcoming 1.7 beta release. The specific APIs which changed were:

Stabilized

* `Path::strip_prefix` (renamed from `relative_from`)
* `path::StripPrefixError` (new error type returned from `strip_prefix`)
* `Ipv4Addr::is_loopback`
* `Ipv4Addr::is_private`
* `Ipv4Addr::is_link_local`
* `Ipv4Addr::is_multicast`
* `Ipv4Addr::is_broadcast`
* `Ipv4Addr::is_documentation`
* `Ipv6Addr::is_unspecified`
* `Ipv6Addr::is_loopback`
* `Ipv6Addr::is_unique_local`
* `Ipv6Addr::is_multicast`
* `Vec::as_slice`
* `Vec::as_mut_slice`
* `String::as_str`
* `String::as_mut_str`
* `<[T]>::clone_from_slice` - the `usize` return value is removed
* `<[T]>::sort_by_key`
* `i32::checked_rem` (and other signed types)
* `i32::checked_neg` (and other signed types)
* `i32::checked_shl` (and other signed types)
* `i32::checked_shr` (and other signed types)
* `i32::saturating_mul` (and other signed types)
* `i32::overflowing_add` (and other signed types)
* `i32::overflowing_sub` (and other signed types)
* `i32::overflowing_mul` (and other signed types)
* `i32::overflowing_div` (and other signed types)
* `i32::overflowing_rem` (and other signed types)
* `i32::overflowing_neg` (and other signed types)
* `i32::overflowing_shl` (and other signed types)
* `i32::overflowing_shr` (and other signed types)
* `u32::checked_rem` (and other unsigned types)
* `u32::checked_neg` (and other unsigned types)
* `u32::checked_shl` (and other unsigned types)
* `u32::saturating_mul` (and other unsigned types)
* `u32::overflowing_add` (and other unsigned types)
* `u32::overflowing_sub` (and other unsigned types)
* `u32::overflowing_mul` (and other unsigned types)
* `u32::overflowing_div` (and other unsigned types)
* `u32::overflowing_rem` (and other unsigned types)
* `u32::overflowing_neg` (and other unsigned types)
* `u32::overflowing_shl` (and other unsigned types)
* `u32::overflowing_shr` (and other unsigned types)
* `ffi::IntoStringError`
* `CString::into_string`
* `CString::into_bytes`
* `CString::into_bytes_with_nul`
* `From<CString> for Vec<u8>`
* `From<CString> for Vec<u8>`
* `IntoStringError::into_cstring`
* `IntoStringError::utf8_error`
* `Error for IntoStringError`

Deprecated

* `Path::relative_from` - renamed to `strip_prefix`
* `Path::prefix` - use `components().next()` instead
* `os::unix::fs` constants - moved to the `libc` crate
* `fmt::{radix, Radix, RadixFmt}` - not used enough to stabilize
* `IntoCow` - conflicts with `Into` and may come back later
* `i32::{BITS, BYTES}` (and other integers) - not pulling their weight
* `DebugTuple::formatter` - will be removed
* `sync::Semaphore` - not used enough and confused with system semaphores

Closes #23284
cc #27709 (still lots more methods though)
Closes #27712
Closes #27722
Closes #27728
Closes #27735
Closes #27729
Closes #27755
Closes #27782
Closes #27798

this makes sure the checks run before typeck (which might use the constant or const
function to calculate an array length) and gives prettier error messages in case of for
loops and such (since they aren't expanded yet).

along with a README explaining how they are to be used

Lots of cruft to remove!

With this commit, metadata encoding and decoding can make use of
thread-local encoding and decoding contexts. These allow implementers
of serialize::Encodable and Decodable to access information and
datastructures that would otherwise not be available to them. For
example, we can automatically translate def-id and span information
during decoding because the decoding context knows which crate the
data is decoded from. Or it allows to make ty::Ty decodable because
the context has access to the ty::ctxt that is needed for creating
ty::Ty instances.

This commit is the standard API stabilization commit for the 1.6 release cycle.
The list of issues and APIs below have all been through their cycle-long FCP and
the libs team decisions are listed below

Stabilized APIs

* `Read::read_exact`
* `ErrorKind::UnexpectedEof` (renamed from `UnexpectedEOF`)
* libcore -- this was a bit of a nuanced stabilization, the crate itself is now
  marked as `#[stable]` and the methods appearing via traits for primitives like
  `char` and `str` are now also marked as stable. Note that the extension traits
  themeselves are marked as unstable as they're imported via the prelude. The
  `try!` macro was also moved from the standard library into libcore to have the
  same interface. Otherwise the functions all have copied stability from the
  standard library now.
* The `#![no_std]` attribute
* `fs::DirBuilder`
* `fs::DirBuilder::new`
* `fs::DirBuilder::recursive`
* `fs::DirBuilder::create`
* `os::unix::fs::DirBuilderExt`
* `os::unix::fs::DirBuilderExt::mode`
* `vec::Drain`
* `vec::Vec::drain`
* `string::Drain`
* `string::String::drain`
* `vec_deque::Drain`
* `vec_deque::VecDeque::drain`
* `collections::hash_map::Drain`
* `collections::hash_map::HashMap::drain`
* `collections::hash_set::Drain`
* `collections::hash_set::HashSet::drain`
* `collections::binary_heap::Drain`
* `collections::binary_heap::BinaryHeap::drain`
* `Vec::extend_from_slice` (renamed from `push_all`)
* `Mutex::get_mut`
* `Mutex::into_inner`
* `RwLock::get_mut`
* `RwLock::into_inner`
* `Iterator::min_by_key` (renamed from `min_by`)
* `Iterator::max_by_key` (renamed from `max_by`)

Deprecated APIs

* `ErrorKind::UnexpectedEOF` (renamed to `UnexpectedEof`)
* `OsString::from_bytes`
* `OsStr::to_cstring`
* `OsStr::to_bytes`
* `fs::walk_dir` and `fs::WalkDir`
* `path::Components::peek`
* `slice::bytes::MutableByteVector`
* `slice::bytes::copy_memory`
* `Vec::push_all` (renamed to `extend_from_slice`)
* `Duration::span`
* `IpAddr`
* `SocketAddr::ip`
* `Read::tee`
* `io::Tee`
* `Write::broadcast`
* `io::Broadcast`
* `Iterator::min_by` (renamed to `min_by_key`)
* `Iterator::max_by` (renamed to `max_by_key`)
* `net::lookup_addr`

New APIs (still unstable)

* `<[T]>::sort_by_key` (added to mirror `min_by_key`)

Closes #27585
Closes #27704
Closes #27707
Closes #27710
Closes #27711
Closes #27727
Closes #27740
Closes #27744
Closes #27799
Closes #27801
cc #27801 (doesn't close as `Chars` is still unstable)
Closes #28968

This is done mostly so that we can refer to MIR types in csearch and other metadata related area.

tests & rustdoc still broken

this is a [breaking-change] to all plugin authors - sorry

This commit stabilizes and deprecates library APIs whose FCP has closed in the
last cycle, specifically:

Stabilized APIs:

* `fs::canonicalize`
* `Path::{metadata, symlink_metadata, canonicalize, read_link, read_dir, exists,
   is_file, is_dir}` - all moved to inherent methods from the `PathExt` trait.
* `Formatter::fill`
* `Formatter::width`
* `Formatter::precision`
* `Formatter::sign_plus`
* `Formatter::sign_minus`
* `Formatter::alternate`
* `Formatter::sign_aware_zero_pad`
* `string::ParseError`
* `Utf8Error::valid_up_to`
* `Iterator::{cmp, partial_cmp, eq, ne, lt, le, gt, ge}`
* `<[T]>::split_{first,last}{,_mut}`
* `Condvar::wait_timeout` - note that `wait_timeout_ms` is not yet deprecated
  but will be once 1.5 is released.
* `str::{R,}MatchIndices`
* `str::{r,}match_indices`
* `char::from_u32_unchecked`
* `VecDeque::insert`
* `VecDeque::shrink_to_fit`
* `VecDeque::as_slices`
* `VecDeque::as_mut_slices`
* `VecDeque::swap_remove_front` - (renamed from `swap_front_remove`)
* `VecDeque::swap_remove_back` - (renamed from `swap_back_remove`)
* `Vec::resize`
* `str::slice_mut_unchecked`
* `FileTypeExt`
* `FileTypeExt::{is_block_device, is_char_device, is_fifo, is_socket}`
* `BinaryHeap::from` - `from_vec` deprecated in favor of this
* `BinaryHeap::into_vec` - plus a `Into` impl
* `BinaryHeap::into_sorted_vec`

Deprecated APIs

* `slice::ref_slice`
* `slice::mut_ref_slice`
* `iter::{range_inclusive, RangeInclusive}`
* `std::dynamic_lib`

Closes #27706
Closes #27725
cc #27726 (align not stabilized yet)
Closes #27734
Closes #27737
Closes #27742
Closes #27743
Closes #27772
Closes #27774
Closes #27777
Closes #27781
cc #27788 (a few remaining methods though)
Closes #27790
Closes #27793
Closes #27796
Closes #27810
cc #28147 (not all parts stabilized)

Fixes #28776

The FCP is coming to a close and 1.4 is coming out soon, so this brings in the
libs team decision for all library features this cycle.

Stabilized APIs:

* `<Box<str>>::into_string`
* `Arc::downgrade`
* `Arc::get_mut`
* `Arc::make_mut`
* `Arc::try_unwrap`
* `Box::from_raw`
* `Box::into_raw`
* `CStr::to_str`
* `CStr::to_string_lossy`
* `CString::from_raw`
* `CString::into_raw`
* `IntoRawFd::into_raw_fd`
* `IntoRawFd`
* `IntoRawHandle::into_raw_handle`
* `IntoRawHandle`
* `IntoRawSocket::into_raw_socket`
* `IntoRawSocket`
* `Rc::downgrade`
* `Rc::get_mut`
* `Rc::make_mut`
* `Rc::try_unwrap`
* `Result::expect`
* `String::into_boxed_slice`
* `TcpSocket::read_timeout`
* `TcpSocket::set_read_timeout`
* `TcpSocket::set_write_timeout`
* `TcpSocket::write_timeout`
* `UdpSocket::read_timeout`
* `UdpSocket::set_read_timeout`
* `UdpSocket::set_write_timeout`
* `UdpSocket::write_timeout`
* `Vec::append`
* `Vec::split_off`
* `VecDeque::append`
* `VecDeque::retain`
* `VecDeque::split_off`
* `rc::Weak::upgrade`
* `rc::Weak`
* `slice::Iter::as_slice`
* `slice::IterMut::into_slice`
* `str::CharIndices::as_str`
* `str::Chars::as_str`
* `str::split_at_mut`
* `str::split_at`
* `sync::Weak::upgrade`
* `sync::Weak`
* `thread::park_timeout`
* `thread::sleep`

Deprecated APIs

* `BTreeMap::with_b`
* `BTreeSet::with_b`
* `Option::as_mut_slice`
* `Option::as_slice`
* `Result::as_mut_slice`
* `Result::as_slice`
* `f32::from_str_radix`
* `f64::from_str_radix`

Closes #27277
Closes #27718
Closes #27736
Closes #27764
Closes #27765
Closes #27766
Closes #27767
Closes #27768
Closes #27769
Closes #27771
Closes #27773
Closes #27775
Closes #27776
Closes #27785
Closes #27792
Closes #27795
Closes #27797

this improves the compilation time for small crates by ~20%