Hard-float (unlike mips32 musl targets but consistent with any other
musl target), MIPS64r2, n64 ABI.

The triples are renamed to carry the `abi64` ABI suffix found on all
other MIPS64 targets, for consistency and forward compatibility, should
Rust gain support for the n32 ABI one day.

This fixes handling default configuration for the `crate_blacklist`
RLS configuration.

Technically this isn't needed, as the VS Code extension can be
configured to accept a predefined blacklist that's equal to the default
one but it's best that it also lands so that we don't need to work
around that.

cc rust-lang#63472

…mangling.

Add UWP MSVC targets

Hi,

- The README URI change is the correct one for VS2019 community edition, which I suspect most people would use. Doesn't _need_ to be merged though.
- This rust-lang@5e6619e fixes the UWP build (msvc or not, doesn't matter). I suspect it broke with recent changes unnoticed because no CI.
- Store lib location is found through the VCToolsInstallDir env variable. The end of the path is currently for the VS2019 store lib locations only.
- I could not test the aarch64_uwp_windows_msvc target because the rust build script does not currently support arm64 msvc AFAIU.

…ichton

Add builtin targets for mips64(el)-unknown-linux-muslabi64

This is prerequisite for rust-lang/libc#1449.

Tested locally to produce working static and dynamic binaries, ~~but CI config is untested for now~~ CI is to be added in a follow-up PR.

*edit: dynamic binaries also confirmed working!*

*edit 2: changed triples to include ABI, and removed stray `crt_static_default = false` declarations to be consistent with other musl targets*

Adapt AddRetag for shallow retagging

With rust-lang/miri#872, Miri only retags "bare" references, not those nested in compound types. This adjust `Retag` statement generation to don't emit retags if they are definitely not a bare reference.

I also expanded the mir-opt test to cover the `Retag` in the drop shim, which had previously not been tested.

…xcrichton

Utilize -Zbinary-dep-depinfo in rustbuild

The last commit moves us over to using binary-dep-depinfo while the first two permit us to bootstrap from what will become future beta, to be released in the next week (it's the `cfg(bootstrap)` processing).

We no longer utilize stamp-file mtimes at all inside rustbuild, and a future PR may be able to entirely eliminate them by eagerly copying to the appropriate sysroot. The only mtime-based dependency tracking left is for documentation because we lie to Cargo about the rustdoc binary, so Cargo does not track changes to the real binary, and codegen-backends because binary-dep-depinfo does not emit that information into the depfiles.

Both of these are fixable in the longer term but this existing patch gives us the following benefits:
 * We no longer delete Cargo target directories manually within a stage. Cross-stage, changes to codegen backends will still clear out target directories. This means that incremental state persists across individual steps (e.g., rebuilding libstd does not clear out librustc incremental state). Fixes rust-lang#54712.
 * Dependency tracking across steps within a given stage is now fully precise. We will not clear out all codegen backend dependencies due to changes in librustc_driver, for example, only deleting the final librustc_codegen_llvm crate. Fixes rust-lang#54008, fixes rust-lang#50481.
 * We properly track codegen backends as a dependency (equivalent to rustc) across changes. Fixes rust-lang#53284, and fixes rust-lang#52719.
 * Cross-stage dependency tracking of crates is also much more accurate and reliable. Most likely fixes rust-lang#49979 (but no reproduction steps in that issue). Fixes rust-lang#59105.

cc rust-lang#63012

Update RLS

This fixes handling default configuration for the `crate_blacklist`
RLS configuration.

Technically this isn't needed, as the VS Code extension can be
configured to accept a predefined blacklist that's equal to the default
one but it's best that it also lands so that we don't need to work
around that.

Without this, manually passing a `null` value as the configuration
unfortunately crashes the RLS. This is the last fix related to configuration.

cc rust-lang#63472

r? @Mark-Simulacrum

rustc_codegen_utils: account for 1-indexed anonymous lifetimes in v0 mangling.

I don't really understand why `anonymize_late_bound_regions` starts with `BrAnon(1)` instead of `BrAnon(0)`, but it does (maybe @nikomatsakis knows?): https://github.com/rust-lang/rust/blob/c43d03a19f326f4a323569328cc501e86eb6d22e/src/librustc/ty/fold.rs#L696-L712

Thankfully, the mangling format and demangler implementations are fine, and I just needed to offset the anonymized lifetime indices by `1` to get the correct mangling.

cc @alexcrichton @michaelwoerister

remove unused Level::PhaseFatal

r? @estebank

Test HRTB issue accepted by compiler

Hi! First Rust PR, so if anything needs changing just let me know and I'll take care of it right away.

Closes rust-lang#50301 which was marked E-needstest