Rollup merge of #78947 - dalance:llvm_cov, r=Mark-Simulacrum
Rollup merge of #78947 - dalance:llvm_cov, r=Mark-Simulacrum

Ship llvm-cov through llvm-tools

`llvm-cov` is used to generate coverage report with LLVM InstrProf-based code coverage #34701.
So if `llvm-cov` is shipped through llvm-tools, users can try it easily accorging to the instruction of [The Rust Unstable Book](https://doc.rust-lang.org/nightly/unstable-book/compiler-flags/source-based-code-coverage.html).

aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,graydon/rust,aidancully/rust