Enable rust-lld on dist-x86_64-musl

Add rust-lld to rustup llvm-tools-preview on nightly for musl

I am using a musl distro on my workstation, with `RUSTFLAGS="-C target-feature=-crt-static"` this works fine. I know that `x86_64-unknown-linux-musl` was originally only meant as a target and not as a host. But most problems have been fixed, and I have fewer problems with `unknown` (rustup) than when I am using `x86_64-alpine-linux-musl` (rust installed by the distro). The only thing I am missing is rust-lld in llvm-tools-preview on nightly.

I needed rust-lld for a wasm tutorial. I built rust-lld and tested it with that tutorial, and it worked well. I asked [here](https://users.rust-lang.org/t/enable-rust-lld-on-x86-64-unknown-linux-musl/39851) where to request to enable lld and ended up doing this PR.

I compared llvm-tools-preview `nightly-x86_64-unknown-linux-musl` and `nightly-x86_64-unknown-linux-gnu`: only rust-lld is missing in musl.

I tested the change using:

```bash
./src/ci/docker/run.sh dist-x86_64-musl
```

And I checked that the resulting rust-lld binary runs.

Add utility to find locals that don't use `StorageLive` annotations and use it for `MaybeStorageLive`

Addresses https://github.com/rust-lang/rust/pull/70004#issuecomment-599271717 (cc @RalfJung).

The only dataflow analysis that is incorrect in this case is `MaybeStorageLive`. `transform/generator.rs` implemented custom handling for this class of locals, but other consumers of this analysis (there's one in [clippy](https://github.com/rust-lang/rust-clippy/blob/513b46793e98ce5b412d388a91f6371d6a9b290b/clippy_lints/src/redundant_clone.rs#L402)) would be incorrect.

r? @tmandry

librustc_hir: return LocalDefId instead of DefId in local_def_id

Its a first try to remove a few calls to `expect_local` and use `LocalDefId` instead of `DefId` where possible for #70853

This adds some calls to `.to_def_id()` to get a `DefId` back when needed. I don't know if I should push `LocalDefId` even further and change, for example, `Res::Def` to accept a `LocalDefId` instead of a `DefId` as second argument.

cc @ecstatic-morse

Rollup of 5 pull requests

Successful merges:

 - #70897 (bump Miri)
 - #70900 (Update cargo)
 - #70902 (Update Clippy)
 - #70939 (Add two const generics regression tests)
 - #70958 (Disable try_reserve tests on Android)

Failed merges:

r? @ghost

Before, it ignored the first argument and marked all variables without
`Storage*` annotations as dead.

Disable try_reserve tests on Android

Calling `realloc` with large sizes seems to be broken on older Android versions that use dlmalloc as the default allocator. This is not an issue for modern Android versions that use jemalloc.

Fixes #55861

Add two const generics regression tests

Closes https://github.com/rust-lang/rust/issues/66596.
Closes https://github.com/rust-lang/rust/issues/61522.

Update Clippy

Closes #70875

Update cargo

4 commits in 6e07d2dfb7fc87b1c9489de41da4dafa239daf03..390e8f245ef2cd7ac698b8a76abf029f9abcab0d
2020-03-31 03:22:39 +0000 to 2020-04-07 17:46:45 +0000
- Compatibility for rust-lang/rust#69926 (rust-lang/cargo#8080)
- Add note about converting triple case in environment variables (rust-lang/cargo#8079)
- Add support for `-Cembed-bitcode=no` (rust-lang/cargo#8066)
- Add triagebot configuration (rust-lang/cargo#8059)

bump Miri

r? @ghost Cc @rust-lang/miri

Fixes https://github.com/rust-lang/rust/issues/70894

Rollup of 7 pull requests

Successful merges:

 - #67705 (Use unrolled loop for searching NULL in [u16] on Windows)
 - #70367 (save/restore `pessimistic_yield` when entering bodies)
 - #70822 (Don't lint for self-recursion when the function can diverge)
 - #70868 (rustc_codegen_ssa: Refactor construction of linker arguments)
 - #70896 (Implement Chain with Option fuses)
 - #70916 (Support `#[track_caller]` on functions in `extern "Rust" { ... }`)
 - #70918 (rustc_session: forbid lints override regardless of position)

Failed merges:

r? @ghost

rustc_session: forbid lints override regardless of position

Addresses the regression reported in #70819 for command line arguments, but does not address the source code flag regression.

Support `#[track_caller]` on functions in `extern "Rust" { ... }`

Fixes https://github.com/rust-lang/rust/issues/70830 which is the follow-up to @EddyB's suggestion in https://github.com/rust-lang/rust/pull/69251#discussion_r380791634 to allow `#[track_caller]` on `fn`s in FFI imports, that is, on functions in `extern "Rust" { ... }` blocks.

This requires that the other side, the FFI export, also have the `#[track_caller]` attribute. Otherwise, undefined behavior is triggered and the blame lies, as usual, with the `unsafe { ... }` block which called the FFI imported function.

After this PR, all forms of `fn` items with the right ABI (`"Rust"`) support `#[track_caller]`.

As a drive-by, the PR also hardens the check rejecting `#[naked] #[track_caller]` such that methods and other forms of `fn` items are also considered.

r? @EddyB
cc @rust-lang/lang

Implement Chain with Option fuses

The iterators are now "fused" with `Option` so we don't need separate state to track which part is already exhausted, and we may also get niche layout for `None`. We don't use the real `Fuse` adapter because its specialization for `FusedIterator` unconditionally descends into the iterator, and that could be expensive to keep revisiting stuff like nested chains. It also hurts compiler performance to add more iterator layers to `Chain`.

This change was inspired by the [proposal](https://internals.rust-lang.org/t/proposal-implement-iter-chain-using-fuse/12006) on the internals forum. This is an alternate to #70332, directly employing some of the same `Fuse` optimizations as #70366 and #70750.

r? @scottmcm

rustc_codegen_ssa: Refactor construction of linker arguments

And add comments.

This PR doesn't reorder any linker arguments and therefore shouldn't contain any observable changes.

The next goal here is to
- Factor out order-independent linker arguments in the compiler code and in target specifications and pass them together. Such arguments generally apply to the whole linking session or the produced linking result rather to individual object files or libraries.
- Figure out where exactly among the remaining order-dependent arguments we should place customization points like `-C link-args` and `-Z pre-link-args`.
- Possibly provide command line opt-outs for options that are currently passed unconditionally (like CRT objects or arguments defined by the target spec).
- Document and stabilize the customization points that are not yet stable (https://github.com/rust-lang/rust/pull/70505).

Don't lint for self-recursion when the function can diverge

Fixes https://github.com/rust-lang/rust/issues/54444

save/restore `pessimistic_yield` when entering bodies

This flag is used to make the execution order around `+=` operators
pessimistic. Failure to save/restore the flag was causing independent
async blocks to effect one another, leading to strange ICEs and failed
assumptions.

Fixes #69307

r? @Zoxc

Use unrolled loop for searching NULL in [u16] on Windows

remove `KEEP_IN_LOCAL_TCX` flag

closes #70285

I did not rename `needs_infer` here as this complex enough as is.
Will probably open a followup for that.

r? @EddyB

Rollup of 7 pull requests

Successful merges:

 - #70134 (add basic support of OsStrExt for HermitCore)
 - #70565 (Add inline attributes for functions used in the query system)
 - #70828 (rustdoc: Don't try to load source files from external crates)
 - #70870 (Fix abuses of tykind::err)
 - #70906 (Suggest move for closures and async blocks in more cases.)
 - #70912 (Do not suggest adding type param when `use` is already suggested)
 - #70930 (add tracking issue to `VecDeque::make_contiguous`)

Failed merges:

r? @ghost

add tracking issue to `VecDeque::make_contiguous`

The tracking issue is https://github.com/rust-lang/rust/issues/70929

Do not suggest adding type param when `use` is already suggested

Fix #70365, cc #70572.

Suggest move for closures and async blocks in more cases.

Fixes #66107, also improves #67577
Related PR https://github.com/rust-lang/rust/pull/65166

Fix abuses of tykind::err

r? @EddyB

cc https://github.com/rust-lang/rust/issues/70866

rustdoc: Don't try to load source files from external crates

Local items defined in external macros shouldn't generate rendered source files and should link to the external crate's docs instead.

Part of #70757

r? @GuillaumeGomez
cc @EddyB

Add inline attributes for functions used in the query system

add basic support of OsStrExt for HermitCore

- this patch increases the compatibility to other operating systems
- in principle `ffi.rs` is derived from `src/libstd/sys/unix/ext/ffi.rs`