Revert "Use workspace lints for crates in compiler/ #138084"

Revert <https://github.com/rust-lang/rust/pull/138084> to buy time to
consider options that avoids breaking downstream usages of cargo on
distributed `rustc-src` artifacts, where such cargo invocations fail due
to inability to inherit `lints` from workspace root manifest's
`workspace.lints` (this is only valid for the source rust-lang/rust
workspace, but not really the distributed `rustc-src` artifacts).

This breakage was reported in
<https://github.com/rust-lang/rust/issues/138304>.

This reverts commit 48caf81484, reversing
changes made to c6662879b2.

compiler/rustc_codegen_ssa/Cargo.toml

@@ -63,6 +63,3 @@ features = ["read_core", "elf", "macho", "pe", "xcoff", "unaligned", "archive",
 [target.'cfg(windows)'.dependencies.windows]
 version = "0.59.0"
 features = ["Win32_Globalization"]
-
-[lints]
-workspace = true

compiler/rustc_codegen_ssa/src/lib.rs

@@ -14,6 +14,7 @@
 #![feature(rustdoc_internals)]
 #![feature(trait_alias)]
 #![feature(try_blocks)]
+#![warn(unreachable_pub)]
 // tidy-alphabetical-end
 
 //! This crate contains codegen code that is used by all codegen backends (LLVM and others).