This reverts commit c6e3d7fa, reversing
changes made to 4591a245.

See https://github.com/rust-lang/rust/issues/47115#issuecomment-403090815
and https://github.com/rust-lang/rust/issues/47115#issuecomment-424053547

Co-authored-by: nikomatsakis

It contains the re-exports that are in `std::prelude::v1`
but not in `core::prelude::v1`.

Calling it prelude is somewhat of a misnomer since (unlike those modules
in `std` or `core`) its contents are never implicitly imported in modules.
Rather it is intended to be used with an explicit glob import like
`use alloc::prelude::*;`.
However there is precedent for the same misnomer with `std::io::prelude`,
for example.

This new module is unstable with the same feature name as the `alloc` care.
They are proposed for stabilization together in RFC
https://github.com/rust-lang/rfcs/pull/2480

closes #45085

this commit adds an `atomic_cas` target option and an unstable `#[cfg(target_has_atomic_cas)]`
attribute to enable a subset of the `Atomic*` API on architectures that don't support atomic CAS
natively, like MSP430 and ARMv6-M.

… since `std` has no corresponding reexports.

Use `alloc::vec::Vec` and `alloc::string::String` instead.

This matches std::collections

Tracking issue FCP: https://github.com/rust-lang/rust/issues/43036#issuecomment-394094318
Reference PR: https://github.com/rust-lang-nursery/reference/pull/353

The heap.rs file was already unused.

Fixes #35729

According to recommendations in
https://github.com/rust-lang/rust/issues/35729#issuecomment-377784884

Tracking issue: https://github.com/rust-lang/rust/issues/49137

Added new()/start()/end() methods to RangeInclusive.

Changed the lowering of `..=` to use RangeInclusive::new().

This is in the matter of RFC 1940 and tracking issue #43302.