Make some NullablePointer enums FFI-compatible with the base pointer type.
librustc: Separate NullablePointer into RawNullablePointer and StructWrappedNullablePointer.
std: Refactor liballoc out of lib{std,sync}

This commit is part of the libstd facade RFC, issue #13851. This creates a new
library, liballoc, which is intended to be the core allocation library for all
of Rust. It is pinned on the basic assumption that an allocation failure is an
abort or failure.

This module has inherited the heap/libc_heap modules from std::rt, the owned/rc
modules from std, and the arc module from libsync. These three pointers are
currently the three most core pointer implementations in Rust.

The UnsafeArc type in std::sync should be considered deprecated and replaced by
Arc<Unsafe<T>>. This commit does not currently migrate to this type, but future
commits will continue this refactoring.
Register new snapshots
auto merge of #14230 : alexcrichton/rust/liballoc, r=cmr,huonw

This commit is part of the libstd facade RFC, issue #13851. This creates a new
library, liballoc, which is intended to be the core allocation library for all
of Rust. It is pinned on the basic assumption that an allocation failure is an
abort or failure.

This module has inherited the heap/libc_heap modules from std::rt, the owned/rc
modules from std, and the arc module from libsync. These three pointers are
currently the three most core pointer implementations in Rust.

The UnsafeArc type in std::sync should be considered deprecated and replaced by
`Arc<Unsafe<T>>`. This commit does not currently migrate to this type, but future
commits will continue this refactoring.
core: Clarify the documentation on core's prelude

Closes #14246
auto merge of #14249 : alexcrichton/rust/issue-14246, r=huonw

Closes #14246
Update debuginfo tests.
auto merge of #14121 : luqmana/rust/option-ffi, r=alexcrichton

This slightly adjusts the NullablePointer representation for some enums in the case where the non-nullable variant has a single field (the ptr field) to be just that, the pointer. This is in contrast to the current behaviour where we'd wrap that single pointer in a LLVM struct.

Fixes #11040 & #11303.