improve the way bootstrap handles rustlib components

When CI rustc is enabled, bootstrap tries to symlink the rust source (project root) into target sysroot right before copying it from the CI rustc's sysroot. This becomes a problem in CI builders (which we currently don't see because they don't use CI rustc) because the copying part will fail as [they run on read-only mode](https://github.com/rust-lang/rust/blob/ef3d6fd7002500af0a985f70d3ac5152623c1396/src/ci/docker/run.sh#L233).

This change fixes the problem by copying `rustc-src` from the CI rustc sysroot and only symlinking `rustc-src` from the rust source when download-rustc is not enabled.

r? `@Kobzol` (we talked about this already on Zulip, he knows the context)

Blocker for rust-lang#122709

…llaumeGomez

Rollup of 7 pull requests

Successful merges:

 - rust-lang#126753 (Add nightly style guide section for `precise_capturing` `use<>` syntax)
 - rust-lang#126880 (Migrate `volatile-intrinsics`, `weird-output-filenames`, `wasm-override-linker`, `wasm-exceptions-nostd` to `rmake`)
 - rust-lang#126941 (Migrate `run-make/llvm-ident` to `rmake.rs`)
 - rust-lang#127128 (Stabilize `duration_abs_diff`)
 - rust-lang#127129 (Use full expr span for return suggestion on type error/ambiguity)
 - rust-lang#127188 ( improve the way bootstrap handles rustlib components)
 - rust-lang#127201 (Improve run-make-support API)

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

…llaumeGomez

Rollup of 8 pull requests

Successful merges:

 - rust-lang#126732 (Stabilize `PanicInfo::message()` and `PanicMessage`)
 - rust-lang#126753 (Add nightly style guide section for `precise_capturing` `use<>` syntax)
 - rust-lang#126832 (linker: Refactor interface for passing arguments to linker)
 - rust-lang#126880 (Migrate `volatile-intrinsics`, `weird-output-filenames`, `wasm-override-linker`, `wasm-exceptions-nostd` to `rmake`)
 - rust-lang#127128 (Stabilize `duration_abs_diff`)
 - rust-lang#127129 (Use full expr span for return suggestion on type error/ambiguity)
 - rust-lang#127188 ( improve the way bootstrap handles rustlib components)
 - rust-lang#127201 (Improve run-make-support API)

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

Rollup merge of rust-lang#127188 - onur-ozkan:rustc-src-fix, r=Kobzol

 improve the way bootstrap handles rustlib components

When CI rustc is enabled, bootstrap tries to symlink the rust source (project root) into target sysroot right before copying it from the CI rustc's sysroot. This becomes a problem in CI builders (which we currently don't see because they don't use CI rustc) because the copying part will fail as [they run on read-only mode](https://github.com/rust-lang/rust/blob/ef3d6fd7002500af0a985f70d3ac5152623c1396/src/ci/docker/run.sh#L233).

This change fixes the problem by copying `rustc-src` from the CI rustc sysroot and only symlinking `rustc-src` from the rust source when download-rustc is not enabled.

r? ``@Kobzol`` (we talked about this already on Zulip, he knows the context)

Blocker for rust-lang#122709

Since rust-lang#127188, copying files from `.rustc-dev-contents`
regressed rust-lang#108767 again. Since `rustc-src` is already
included in the CI rustc sysroot, we don't need to copy these files to have `rustc-src` component.

Signed-off-by: onur-ozkan <work@onurozkan.dev>

…, r=Kobzol

don't copy `.rustc-dev-contents` from CI rustc

Since rust-lang#127188, copying files from `.rustc-dev-contents` regressed rust-lang#108767 again. Since `rustc-src` is already included in the CI rustc sysroot, we don't need to copy these files to have `rustc-src` component.

Blocker for rust-lang#122709

Rollup merge of rust-lang#129311 - onur-ozkan:multiple-candidates-fix, r=Kobzol

don't copy `.rustc-dev-contents` from CI rustc

Since rust-lang#127188, copying files from `.rustc-dev-contents` regressed rust-lang#108767 again. Since `rustc-src` is already included in the CI rustc sysroot, we don't need to copy these files to have `rustc-src` component.

Blocker for rust-lang#122709