Don't build the `rust-demangler` binary for coverage tests

The coverage-run tests invoke `llvm-cov`, which requires us to specify a command-line demangler that it can use to demangle Rust symbol names.

Historically this used `src/tools/rust-demangler`, which means that we currently build two different command-line tools to help with the coverage tests (`rust-demangler` and `coverage-dump`).

However, it occurred to me that if we add a demangler mode to `coverage-dump` (which is only a handful of lines and no extra dependencies), then we only need to build one helper binary for the coverage tests, and there is no need for tests to build `rust-demangler` at all.

---

Note that the `rust-demangler` binary is separate from the `rustc-demangle` crate (which both `rust-demangler` and `coverage-dump` use as a dependency to do the actual demangling).

---

So the main benefits/motivations here are:
- Slightly faster builds after a fresh checkout or bootstrap bump.
- Making it clear that currently no tests actually need the `rust-demangler` binary, since the coverage tests can use their own tool instead.

Rollup of 6 pull requests

Successful merges:

 - rust-lang#125652 (Revert propagation of drop-live information from Polonius)
 - rust-lang#125730 (Apply `x clippy --fix` and `x fmt` on Rustc)
 - rust-lang#125752 (run-make: enforce `#[must_use]` and arm command wrappers with drop bombs)
 - rust-lang#125756 (coverage: Optionally instrument the RHS of lazy logical operators)
 - rust-lang#125796 (Also InstSimplify `&raw*`)
 - rust-lang#125816 (Don't build the `rust-demangler` binary for coverage tests)

r? `@ghost`
`@rustbot` modify labels: rollup

Don't build the `rust-demangler` binary for coverage tests

The coverage-run tests invoke `llvm-cov`, which requires us to specify a command-line demangler that it can use to demangle Rust symbol names.

Historically this used `src/tools/rust-demangler`, which means that we currently build two different command-line tools to help with the coverage tests (`rust-demangler` and `coverage-dump`).

However, it occurred to me that if we add a demangler mode to `coverage-dump` (which is only a handful of lines and no extra dependencies), then we only need to build one helper binary for the coverage tests, and there is no need for tests to build `rust-demangler` at all.

---

Note that the `rust-demangler` binary is separate from the `rustc-demangle` crate (which both `rust-demangler` and `coverage-dump` use as a dependency to do the actual demangling).

---

So the main benefits/motivations here are:
- Slightly faster builds after a fresh checkout or bootstrap bump.
- Making it clear that currently no tests actually need the `rust-demangler` binary, since the coverage tests can use their own tool instead.

…iaskrgr

Rollup of 7 pull requests

Successful merges:

 - rust-lang#125652 (Revert propagation of drop-live information from Polonius)
 - rust-lang#125730 (Apply `x clippy --fix` and `x fmt` on Rustc)
 - rust-lang#125756 (coverage: Optionally instrument the RHS of lazy logical operators)
 - rust-lang#125776 (Stop using `translate_args` in the new solver)
 - rust-lang#125796 (Also InstSimplify `&raw*`)
 - rust-lang#125807 (Also resolve the type of constants, even if we already turned it into an error constant)
 - rust-lang#125816 (Don't build the `rust-demangler` binary for coverage tests)

r? `@ghost`
`@rustbot` modify labels: rollup

Rollup merge of rust-lang#125816 - Zalathar:demangler, r=oli-obk

Don't build the `rust-demangler` binary for coverage tests

The coverage-run tests invoke `llvm-cov`, which requires us to specify a command-line demangler that it can use to demangle Rust symbol names.

Historically this used `src/tools/rust-demangler`, which means that we currently build two different command-line tools to help with the coverage tests (`rust-demangler` and `coverage-dump`).

However, it occurred to me that if we add a demangler mode to `coverage-dump` (which is only a handful of lines and no extra dependencies), then we only need to build one helper binary for the coverage tests, and there is no need for tests to build `rust-demangler` at all.

---

Note that the `rust-demangler` binary is separate from the `rustc-demangle` crate (which both `rust-demangler` and `coverage-dump` use as a dependency to do the actual demangling).

---

So the main benefits/motivations here are:
- Slightly faster builds after a fresh checkout or bootstrap bump.
- Making it clear that currently no tests actually need the `rust-demangler` binary, since the coverage tests can use their own tool instead.

Remove `src/tools/rust-demangler`

`rust-demangler` is a small binary that reads a list of mangled symbols from stdin, demangles them (using the `rustc-demangle` library crate), and prints the demangled symbols to stdout.

It was added as part of the initial implementation of coverage instrumentation in 2020/2021, so that coverage tests could pass it to `llvm-cov --Xdemangler` when generating coverage reports. It has been largely untouched since then.

As of rust-lang#125816 it is no longer used by coverage tests, and has no remaining in-tree uses.

There is code in bootstrap to build and package the demangler, but it's unclear where the resulting binaries actually end up, or whether there's any reasonable way for `rustup` users to obtain them.

---

For users needing a command-line demangler, `rustfilt` exists and is more actively maintained. It's also quite easy to use the `rustc-demangle` library to build a custom command-line demangler if necessary, with only a few lines of code.

The tool's name (`rust-demangler`) is easily confused with the name of the library crate `rustc-demangle`, so removing the tool will eliminate that confusion. There also doesn't appear to be much reason to use `rust-demangler` over `rustfilt`.

---

This PR therefore removes the tool, and removes all of its associated code from bootstrap.

MCP filed: rust-lang/compiler-team#754

Rollup merge of rust-lang#125880 - Zalathar:demangler, r=oli-obk

Remove `src/tools/rust-demangler`

`rust-demangler` is a small binary that reads a list of mangled symbols from stdin, demangles them (using the `rustc-demangle` library crate), and prints the demangled symbols to stdout.

It was added as part of the initial implementation of coverage instrumentation in 2020/2021, so that coverage tests could pass it to `llvm-cov --Xdemangler` when generating coverage reports. It has been largely untouched since then.

As of rust-lang#125816 it is no longer used by coverage tests, and has no remaining in-tree uses.

There is code in bootstrap to build and package the demangler, but it's unclear where the resulting binaries actually end up, or whether there's any reasonable way for `rustup` users to obtain them.

---

For users needing a command-line demangler, `rustfilt` exists and is more actively maintained. It's also quite easy to use the `rustc-demangle` library to build a custom command-line demangler if necessary, with only a few lines of code.

The tool's name (`rust-demangler`) is easily confused with the name of the library crate `rustc-demangle`, so removing the tool will eliminate that confusion. There also doesn't appear to be much reason to use `rust-demangler` over `rustfilt`.

---

This PR therefore removes the tool, and removes all of its associated code from bootstrap.

MCP filed: rust-lang/compiler-team#754