error: unused import - when building Rust on Solaris where isn't fd-lock available

[psumbera]

error: unused import: `std::fs::OpenOptions`
 --> bin/main.rs:8:5
  |
8 | use std::fs::OpenOptions;
  |     ^^^^^^^^^^^^^^^^^^^^
  |
  = note: `-D unused-imports` implied by `-D warnings`

error: unused import: `std::io::Write`
 --> bin/main.rs:9:5
  |
9 | use std::io::Write;
  |     ^^^^^^^^^^^^^^

error: unused imports: `fs`, `process`
  --> bin/main.rs:10:16
   |
10 | use std::{env, fs, process};
   |                ^^  ^^^^^^^

error: could not compile `bootstrap` due to 3 previous errors
warning: build failed, waiting for other jobs to finish...
Building bootstrap
failed to run: /builds/psumbera/rust-lang-build/build/x86_64-pc-solaris/stage0/bin/cargo build --manifest-path /builds/psumbera/rust-lang-build/src/bootstrap/Cargo.toml
Build completed unsuccessfully in 0:01:26

This is regression from: e7e584b

Prposed fix: #113048