test for the default parallel compiler on threads=2

Author: SparrowLii

compiler/rustc_session/src/options.rs

@@ -1800,7 +1800,7 @@ written to standard error output)"),
     /// in the future. Note that -Zthreads=0 is the way to get
     /// the num_cpus behavior.
     #[rustc_lint_opt_deny_field_access("use `Session::threads` instead of this field")]
-    threads: usize = (1, parse_threads, [UNTRACKED],
+    threads: usize = (2, parse_threads, [UNTRACKED],
         "use a thread pool with N threads"),
     time_llvm_passes: bool = (false, parse_bool, [UNTRACKED],
         "measure time of each LLVM pass (default: no)"),

src/bootstrap/config.rs

@@ -1431,7 +1431,7 @@ impl Config {
             set(&mut config.use_lld, rust.use_lld);
             set(&mut config.lld_enabled, rust.lld);
             set(&mut config.llvm_tools_enabled, rust.llvm_tools);
-            config.rustc_parallel = rust.parallel_compiler.unwrap_or(false);
+            config.rustc_parallel = rust.parallel_compiler.unwrap_or(true);
             config.rustc_default_linker = rust.default_linker;
             config.musl_root = rust.musl_root.map(PathBuf::from);
             config.save_toolstates = rust.save_toolstates.map(PathBuf::from);