Rollup merge of #69965 - mark-i-m:codegen-utils, r=eddyb

Refactorings to get rid of rustc_codegen_utils

r? @eddyb

cc #45276

After this, the only modules left in `rustc_codegen_utils` are
- `link`: a bunch of linking-related functions (many dealing with file names). These are mostly consumed by save analysis, rustc_driver, rustc_interface, and of course codegen. I assume they live here because we don't want a dependency of save analysis on codegen... Perhaps they can be moved to librustc?
- ~`symbol_names` and `symbol_names_test`: honestly it seems odd that `symbol_names_test` is not a submodule of `symbol_names`. It seems like these could honestly live in their own crate or move to librustc. Already name mangling is exported as the `symbol_name` query.~ (move it to its own crate)

I don't mind doing either of the above as part of this PR or a followup if you want.

src/librustc_codegen_llvm/Cargo.toml

@@ -20,7 +20,6 @@ rustc = { path = "../librustc" }
 rustc-demangle = "0.1"
 rustc_attr = { path = "../librustc_attr" }
 rustc_codegen_ssa = { path = "../librustc_codegen_ssa" }
-rustc_codegen_utils = { path = "../librustc_codegen_utils" }
 rustc_data_structures = { path = "../librustc_data_structures" }
 rustc_errors = { path = "../librustc_errors" }
 rustc_feature = { path = "../librustc_feature" }

src/librustc_codegen_llvm/lib.rs

@@ -27,7 +27,6 @@ use rustc_codegen_ssa::back::write::{CodegenContext, FatLTOInput, ModuleConfig};
 use rustc_codegen_ssa::traits::*;
 use rustc_codegen_ssa::ModuleCodegen;
 use rustc_codegen_ssa::{CodegenResults, CompiledModule};
-use rustc_codegen_utils::codegen_backend::CodegenBackend;
 use rustc_errors::{FatalError, Handler};
 use rustc_serialize::json;
 use rustc_session::config::{self, OptLevel, OutputFilenames, PrintRequest};