Rollup merge of rust-lang#109926 - SparrowLii:parallel_log, r=eholk

write threads info into log only when debugging

The current tracing log will unconditionally write thread information during parallel compilation, which sometimes confuses some normal output log information

This fixes the UI test failure of:
```
[ui] tests/ui/consts/const_in_pattern/issue-73431.rs
```
Updates rust-lang#75760

compiler/rustc_log/src/lib.rs

@@ -83,7 +83,7 @@ pub fn init_env_logger(env: &str) -> Result<(), Error> {
         .with_verbose_exit(verbose_entry_exit)
         .with_verbose_entry(verbose_entry_exit)
         .with_indent_amount(2);
-    #[cfg(parallel_compiler)]
+    #[cfg(all(parallel_compiler, debug_assertions))]
     let layer = layer.with_thread_ids(true).with_thread_names(true);
 
     let subscriber = tracing_subscriber::Registry::default().with(filter).with(layer);

src/librustdoc/lib.rs

@@ -203,7 +203,7 @@ fn init_logging() {
         .with_verbose_exit(true)
         .with_verbose_entry(true)
         .with_indent_amount(2);
-    #[cfg(parallel_compiler)]
+    #[cfg(all(parallel_compiler, debug_assertions))]
     let layer = layer.with_thread_ids(true).with_thread_names(true);
 
     use tracing_subscriber::layer::SubscriberExt;