This commit promotes the `wasm32-wasip2` Rust target to tier 2 as
proposed in rust-lang/compiler-team#760. There are two major changes in
this PR:

1. The `dist-various-2` container, which already produces the other WASI
   targets, now has an extra target added for `wasm32-wasip2`.
2. A new `wasm-component-ld` binary is added to all host toolchains when
   LLD is enabled. This is the linker used for the `wasm32-wasip2` target.

This new linker is added for all host toolchains to ensure that all host
toolchains can produce the `wasm32-wasip2` target. This is similar to
how `rust-lld` was originally included for all host toolchains to be
able to produce WebAssembly output when the targets were first added.
The new linker is developed [here][wasm-component-ld] and is pulled in
via a crates.io-based dependency to the tree here.

[wasm-component-ld]: https://github.com/bytecodealliance/wasm-component-ld

Reuse preexisting macro and switch it to a "bootstrap tool" to try to
resolve build issues.

Switch it to using a just-built standard library which enables it to be
cross compiled. Additionally allow it access to `min_specialization`
which `ahash`, a dependency, wants.