Enable -Zthreads=sync by default

Author: petrochenkov

compiler/rustc_session/src/options.rs

@@ -1105,7 +1105,7 @@ pub mod parse {
         // We want to cap the number of threads here to avoid large numbers like 999999 and compiler panics.
         // This solution was suggested here https://github.com/rust-lang/rust/issues/117638#issuecomment-1800925067
         let n = n.min(MAX_THREADS_CAP);
-        *slot = (n > 1).then_some(n); // Enable synchronization if we're using more than one thread.
+        *slot = Some(n);
         true
     }