Previously, it would always treat download-rustc as set to false, which made bootstrap issues with
download-rustc hard to debug.

this was a pre-existing latent bug, we just didn't have any CI builders exercising it.

fixes the following errors:
```
 ---- [ui] tests/ui/sanitize/new-llvm-pass-manager-thin-lto.rs#opt1 stdout ----

error in revision `opt1`: test compilation failed although it shouldn't!
status: exit status: 1
command: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/tests/ui/sanitize/new-llvm-pass-manager-thin-lto.rs" "-Zthreads=1" "-Zsimulate-remapped-rust-src-base=/rustc/FAKE_PREFIX" "-Ztranslate-remapped-path-to-local-path=no" "--sysroot" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2" "--target=i686-unknown-linux-gnu" "--cfg" "opt1" "--error-format" "json" "--json" "future-incompat" "-Ccodegen-units=1" "-Zui-testing" "-Zdeduplicate-diagnostics=no" "-Cstrip=debuginfo" "--remap-path-prefix=/checkout/tests/ui=fake-test-src-base" "-o" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/sanitize/new-llvm-pass-manager-thin-lto.opt1/a" "-A" "unused" "-Crpath" "-Cdebuginfo=0" "-Lnative=/checkout/obj/build/i686-unknown-linux-gnu/native/rust-test-helpers" "-Clinker=x86_64-linux-gnu-gcc" "-L" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/sanitize/new-llvm-pass-manager-thin-lto.opt1/auxiliary" "-Zsanitizer=address" "-Clto=thin" "-Copt-level=1"
--- stderr -------------------------------
error: linking with `x86_64-linux-gnu-gcc` failed: exit status: 1
   = note: x86_64-linux-gnu-gcc: error: /checkout/obj/build/x86_64-unknown-linux-gnu/stage2/lib/rustlib/i686-unknown-linux-gnu/lib/librustc-nightly_rt.asan.a: No such file or directory

failures:
    [ui] tests/ui/sanitize/badfree.rs
    [ui] tests/ui/sanitize/address.rs
    [ui] tests/ui/sanitize/use-after-scope.rs
    [ui] tests/ui/sanitize/new-llvm-pass-manager-thin-lto.rs#opt0
    [ui] tests/ui/sanitize/new-llvm-pass-manager-thin-lto.rs#opt1
```

by using `rustc-builds-alt` if download-rustc is set

this also changes the download code to use a separate build/cache/ directory and .rustc-stamp stamp file depending on whether assertions are enabled.

The style guide gave an example of breaking a multi-line chain element
and all subsequent elements to a new line, but that same example and the
accompanying text also had several chain items stacked on the first
line. rustfmt doesn't do this, except when the rule saying to combine

```
shrt
    .y()
```

into

```
shrt.y()
```

applies.

This reverts commit 08ce68b.

Replace hard-coded values with  GNU_PROPERTY_{X86|AARCH64}_FEATURE_1_AND from the object crate.

…-error.rs

Not only are they a pain to update, but they differ depending on whether `parallel-rustc` is enabled or not

This was not the correct fix. The problem was two-fold:
- `download-rustc` didn't respect `llvm.assertions`
- `rust-dev` was missing a bump to `download-ci-llvm-stamp`

The first is fixed in this PR and the latter was fixed a while ago. Revert this change to avoid breaking `rpath = false`.

…ertlarsan68

various download-rustc fixes

separated out from rust-lang#112143 because it keeps getting stuck in limbo.

best reviewed commit-by-commit

…hains, r=calebcartwright

style-guide: Fix chain example to match rustfmt behavior

The style guide gave an example of breaking a multi-line chain element
and all subsequent elements to a new line, but that same example and the
accompanying text also had several chain items stacked on the first
line. rustfmt doesn't do this, except when the rule saying to combine

```
shrt
    .y()
```

into

```
shrt.y()
```

applies.

This is a bugfix to match rustfmt behavior, so it's not a breaking change, and
it just needs a ``@rust-lang/style`` reviewer to r+.

…-let, r=cjgillot

While let suggestion will work for closure body

Fixes rust-lang#113354

Revert "fix: 🐛 etc/bash_complettion -> src/etc/... to avoid copy …

## why

- [x] revert my broken PR

rust-lang#110906

This reverts commit 08ce68b.

Use constants from object crate

Replace hard-coded values with  `GNU_PROPERTY_{X86|AARCH64}_FEATURE_1_AND` from the object crate.

When working on  [issue](rust-lang#103001) it was suggested that we moved these constants to the object crate .  [PR](gimli-rs/object#537). Now that that the object crate has been updated  [PR](rust-lang#111413) we can make this change.