Rollup merge of rust-lang#74871 - etherealist:musl_doc, r=Mark-Simulacrum

Enable docs on dist-x86_64-musl

Add the `rust-docs` component to toolchain `x86_64-unknown-linux-musl`, which allows people using rustup on their musl-based linux distribution to download the rust-docs.

`--disable-docs` is based on the assumption that `x86_64-unknown-linux-musl` is only a cross-compile target.

I have tested that the docs are built. I assume the build-system will automatically detect the docs and create a `rust-docs` component. I will [monitor](https://rust-lang.github.io/rustup-components-history/x86_64-unknown-linux-musl.html) the components and create a follow-up PR, if the docs aren't published.

See also rust-lang#70619, where we enabled `rust-lld` to enable the wasm-workflow on musl-based linux distributions.

Author: Manishearth

src/ci/docker/host-x86_64/dist-x86_64-musl/Dockerfile

@@ -33,7 +33,6 @@ ENV HOSTS=x86_64-unknown-linux-musl
 ENV RUST_CONFIGURE_ARGS \
       --musl-root-x86_64=/usr/local/x86_64-linux-musl \
       --enable-extended \
-      --disable-docs \
       --enable-lld \
       --set target.x86_64-unknown-linux-musl.crt-static=false \
       --build $HOSTS