[incremental] Collect stats about duplicated edge reads from queries

Part of #45873

Refactor type memory layouts and ABIs, to be more general and easier to optimize.

To combat combinatorial explosion, type layouts are now described through 3 orthogonal properties:
* `Variants` describes the plurality of sum types (where applicable)
  * `Single` is for one inhabited/active variant, including all C `struct`s and `union`s
  * `Tagged` has its variants discriminated by an integer tag, including C `enum`s
  * `NicheFilling` uses otherwise-invalid values ("niches") for all but one of its inhabited variants
* `FieldPlacement` describes the number and memory offsets of fields (if any)
  * `Union` has all its fields at offset `0`
  * `Array` has offsets that are a multiple of its `stride`; guarantees all fields have one type
  * `Arbitrary` records all the field offsets, which can be out-of-order
* `Abi` describes how values of the type should be passed around, including for FFI
  * `Uninhabited` corresponds to no values, associated with unreachable control-flow
  * `Scalar` is ABI-identical to its only integer/floating-point/pointer "scalar component"
  * `ScalarPair` has two "scalar components", but only applies to the Rust ABI
  * `Vector` is for SIMD vectors, typically `#[repr(simd)]` `struct`s in Rust
  * `Aggregate` has arbitrary contents, including all non-transparent C `struct`s and `union`s

Size optimizations implemented so far:
* ignoring uninhabited variants (i.e. containing uninhabited fields), e.g.:
  * `Option<!>` is 0 bytes
  * `Result<T, !>` has the same size as `T`
* using arbitrary niches, not just `0`, to represent a data-less variant, e.g.:
  * `Option<bool>`, `Option<Option<bool>>`, `Option<Ordering>` are all 1 byte
  * `Option<char>` is 4 bytes
* using a range of niches to represent *multiple* data-less variants, e.g.:
  * `enum E { A(bool), B, C, D }` is 1 byte

Code generation now takes advantage of `Scalar` and `ScalarPair` to, in more cases, pass around scalar components as immediates instead of indirectly, through pointers into temporary memory, while avoiding LLVM's "first-class aggregates", and there's more untapped potential here.

Closes #44426, fixes #5977, fixes #14540, fixes #43278.

This reverts commit b12dcdef.

Updated Release notes for 1.22.0

[rendered](https://github.com/Aaronepower/rust/blob/master/RELEASES.md)

Undo the Sized specialization from Iterator::nth

I just added this as part of https://github.com/rust-lang/rust/pull/45595, but I'm now afraid there's a specialization issue with it, since I tried to add [another similar specialization](https://github.com/rust-lang/rust/compare/master...scottmcm:faster-iter-by-ref?expand=1#diff-1398f322bc563592215b583e9b0ba936R2390), and ended up getting really disturbing test failures like
```
thread 'iter::test_by_ref_folds' panicked at 'assertion failed: `(left == right)`
  left: `15`,
 right: `15`', src\libcore\../libcore/tests\iter.rs:1720:4
```

So since this wasn't the most critical part of the change and a new beta is branching within a week, I think putting this part back to what it was before is the best option.

update openssl{,-sys} to fix build with libressl 2.6.x

Update libc to include Fuchsia changes

This is an update of libc to include the updated Fuchsia "open" flags added in https://github.com/rust-lang/libc/pull/849.

cc @smklein
r? @alexcrichton