Rename `lib.rs` to `bindings.rs` and minor BUILD cleanup.

Among other things, this fixes the following warning:

```
warning: found module declaration for lib.rs
  --> third_party/crubit/cc_bindings_from_rs/cc_bindings_from_rs.rs:22:1
   |
22 | mod lib;
   | ^^^^^^^^
   |
   = note: `#[warn(special_module_name)]` on by default
   = note: lib.rs is the root of this crate's library target
   = help: to refer to it from other targets, use the library's name as the path
```
PiperOrigin-RevId: 478108617
diff --git a/cc_bindings_from_rs/BUILD b/cc_bindings_from_rs/BUILD
index d51dc25..a02b304 100644
--- a/cc_bindings_from_rs/BUILD
+++ b/cc_bindings_from_rs/BUILD
@@ -17,9 +17,9 @@
 rust_binary(
     name = "cc_bindings_from_rs",
     srcs = [
+        "bindings.rs",
         "cc_bindings_from_rs.rs",
         "cmdline.rs",
-        "lib.rs",
     ],
     crate_root = "cc_bindings_from_rs.rs",
     # TODO(b/242703401): Remove once cc_common.link works for rustc libraries.
@@ -30,7 +30,6 @@
         "nobuilder",
         "notap",
     ],
-    visibility = ["//:__subpackages__"],
     deps = [
         "//common:rust_allocator_shims",
         "//common:token_stream_printer",
@@ -40,7 +39,6 @@
         "@crate_index//:itertools",
         "@crate_index//:proc-macro2",
         "@crate_index//:quote",
-        "@crate_index//:tracing",
     ],
 )
 
diff --git a/cc_bindings_from_rs/lib.rs b/cc_bindings_from_rs/bindings.rs
similarity index 100%
rename from cc_bindings_from_rs/lib.rs
rename to cc_bindings_from_rs/bindings.rs
diff --git a/cc_bindings_from_rs/cc_bindings_from_rs.rs b/cc_bindings_from_rs/cc_bindings_from_rs.rs
index 9938f03..4f9d53e 100644
--- a/cc_bindings_from_rs/cc_bindings_from_rs.rs
+++ b/cc_bindings_from_rs/cc_bindings_from_rs.rs
@@ -16,18 +16,26 @@
 extern crate rustc_session;
 extern crate rustc_span;
 
-// TODO(lukasza): Make `cmdline` and `lib` a separate crate (once we move to
-// Bazel).
+// TODO(lukasza): Make `bindings` and `cmdline` separate crates (once we move to
+// Bazel).  This hasn't been done that yet, because:
+// * Today it would require replicating `rustc_driver`-related `BUILD` hacks
+//   into additional targets.  And since this particular problem will go away on
+//   its own in Q4 2022 or Q1 2023, maybe for now we can ignore having
+//   multi-source-file crate?
+// * To avoid the ickyness above, one may want to start by making `cmdline.rs`
+//   `rustc_driver`-agnostic first (switching `@herefile` to a `clap`-based,
+//   manually coded behavior).  But this refactoring feels a bit arbitrary and
+//   needs more discussion (maybe we want to keep `@file` support from rustc?).
+mod bindings;
 mod cmdline;
-mod lib;
 
 use anyhow::Context;
 use itertools::Itertools;
 use rustc_middle::ty::TyCtxt;
 use std::path::Path;
 
+use bindings::GeneratedBindings;
 use cmdline::Cmdline;
-use lib::GeneratedBindings;
 use token_stream_printer::tokens_to_string;
 
 /// This mostly wraps and simplifies a subset of APIs from the `rustc_driver`
@@ -39,7 +47,7 @@
     use rustc_interface::Queries;
     use rustc_middle::ty::TyCtxt;
 
-    use crate::lib::enter_tcx;
+    use crate::bindings::enter_tcx;
 
     /// Wrapper around `rustc_driver::RunCompiler::run` that exposes a
     /// simplified API:
@@ -204,7 +212,7 @@
 mod tests {
     use super::run_with_cmdline_args;
 
-    use crate::lib::tests::get_sysroot_for_testing;
+    use crate::bindings::tests::get_sysroot_for_testing;
     use itertools::Itertools;
     use std::path::PathBuf;
     use tempfile::{tempdir, TempDir};