Rollup of 9 pull requests

Successful merges:

 - #145095 (Migrate `UnsizedConstParamTy`  to unstable impl of `ConstParamTy_`)
 - #145960 (Split `FnCtxt::report_args_error` into subfunctions)
 - #146402 (interpret: fix overlapping aggregate initialization)
 - #146466 (llvm-wrapper: other cleanup)
 - #146574 (compiletest: Enable new-output-capture by default)
 - #146599 (replace some `#[const_trait]` with `const trait`)
 - #146601 (compiletest: Make `./x test --test-args ...` work again)
 - #146608 (improve internal bootstrap docs)
 - #146609 (bootstrap: lower verbosity of cargo to one less than bootstrap's)

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

Rollup of 9 pull requests

Successful merges:

 - #145095 (Migrate `UnsizedConstParamTy`  to unstable impl of `ConstParamTy_`)
 - #145960 (Split `FnCtxt::report_args_error` into subfunctions)
 - #146402 (interpret: fix overlapping aggregate initialization)
 - #146466 (llvm-wrapper: other cleanup)
 - #146574 (compiletest: Enable new-output-capture by default)
 - #146599 (replace some `#[const_trait]` with `const trait`)
 - #146601 (compiletest: Make `./x test --test-args ...` work again)
 - #146608 (improve internal bootstrap docs)
 - #146609 (bootstrap: lower verbosity of cargo to one less than bootstrap's)

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

Rollup merge of #146574 - Zalathar:capture, r=jieyouxu

compiletest: Enable new-output-capture by default

The new output-capture implementation was added in #146119, but was disabled by default and required opt-in.

Since then, I haven't encountered any problems in my own testing/usage, and I haven't heard any problem reports from other contributors who might have opted in.

It's unlikely that more opt-in testing will help, so the next step is to enable new-output-capture by default and see if anyone complains. (Hopefully nobody!)

If needed, the new default can be overridden (for now) by setting environment variable `COMPILETEST_NEW_OUTPUT_CAPTURE=off`. Please file an issue (or let me know) if anyone finds a reason to do this.

r? jieyouxu

compiletest: Remove old-output-capture and become a stage0 bootstrap tool

The new compiletest output-capture system became the default in rust-lang#146574, and no problems have been reported since.

This PR therefore removes the old output-capture implementation from compiletest, and adjusts bootstrap to always build and test compiletest as a stage0 bootstrap tool.

In other words, compiletest no longer relies on any unstable features (such as `libtest` or `internal_output_capture`), and is now written entirely in stable Rust!

The compiletest self-tests still need access to an in-tree rustc, in order to obtain information via `rustc --print`, so we interpret `--stage` as indicating the stage of that secondary compiler, but always use the stage0 compiler to build compiletest itself.

r? Kobzol

Rollup merge of #146929 - Zalathar:capture, r=Kobzol,jieyouxu

compiletest: Remove old-output-capture and become a stage0 bootstrap tool

The new compiletest output-capture system became the default in #146574, and no problems have been reported since.

This PR therefore removes the old output-capture implementation from compiletest, and adjusts bootstrap to always build and test compiletest as a stage0 bootstrap tool.

In other words, compiletest no longer relies on any unstable features (such as `libtest` or `internal_output_capture`), and is now written entirely in stable Rust!

The compiletest self-tests still need access to an in-tree rustc, in order to obtain information via `rustc --print`, so we interpret `--stage` as indicating the stage of that secondary compiler, but always use the stage0 compiler to build compiletest itself.

r? Kobzol

Rollup of 9 pull requests

Successful merges:

 - rust-lang#145095 (Migrate `UnsizedConstParamTy`  to unstable impl of `ConstParamTy_`)
 - rust-lang#145960 (Split `FnCtxt::report_args_error` into subfunctions)
 - rust-lang#146402 (interpret: fix overlapping aggregate initialization)
 - rust-lang#146466 (llvm-wrapper: other cleanup)
 - rust-lang#146574 (compiletest: Enable new-output-capture by default)
 - rust-lang#146599 (replace some `#[const_trait]` with `const trait`)
 - rust-lang#146601 (compiletest: Make `./x test --test-args ...` work again)
 - rust-lang#146608 (improve internal bootstrap docs)
 - rust-lang#146609 (bootstrap: lower verbosity of cargo to one less than bootstrap's)

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

compiletest: Remove old-output-capture and become a stage0 bootstrap tool

The new compiletest output-capture system became the default in rust-lang/rust#146574, and no problems have been reported since.

This PR therefore removes the old output-capture implementation from compiletest, and adjusts bootstrap to always build and test compiletest as a stage0 bootstrap tool.

In other words, compiletest no longer relies on any unstable features (such as `libtest` or `internal_output_capture`), and is now written entirely in stable Rust!

The compiletest self-tests still need access to an in-tree rustc, in order to obtain information via `rustc --print`, so we interpret `--stage` as indicating the stage of that secondary compiler, but always use the stage0 compiler to build compiletest itself.

r? Kobzol