Remove the ar git dependency

[bjorn3]

https://github.com/bjorn3/rustc_codegen_cranelift/blob/ab425a4bca1d6df234596a1621c4cabcc73bb272/Cargo.toml#L21

It will break the build if for whatever reason this commit/repo is gone in the future. I could make it a git subtree, but I don't know if git subtree supports nesting.

[bjorn3]

Quoting from https://github.com/bjorn3/rustc_codegen_cranelift/issues/1202:

https://github.com/bjorn3/rustc_codegen_cranelift/pull/1201 changed the Cranelift deps to crates.io releases.

There is still a git dependency on my fork of the ar crate (https://github.com/bjorn3/rust-ar/tree/do_not_remove_cg_clif_ranlib). I think I will need to fix symbol table support for macOS and then poke the maintainer of rust-ar to release a new version of my PR.

[bjorn3]

I have decided to rewrite llvm's archive builder in rust. This should ensure that the produced archives are correct on all platforms supported by LLVM. The resulting crate will be published on crates.io.

https://github.com/llvm/llvm-project/blob/8ef3e895ad8ab1724e2b87cabad1dacdc7a397a3/llvm/lib/Object/ArchiveWriter.cpp

[bjorn3]

rust-lang/rust#97485 will fix this.