fix check_cfg

Author: pietroalbini

src/bootstrap/lib.rs

@@ -198,6 +198,7 @@ const EXTRA_CHECK_CFGS: &[(Option<Mode>, &'static str, Option<&[&'static str]>)]
     (None, "bootstrap", None),
     (Some(Mode::Rustc), "parallel_compiler", None),
     (Some(Mode::ToolRustc), "parallel_compiler", None),
+    (Some(Mode::Codegen), "parallel_compiler", None),
     (Some(Mode::Std), "stdarch_intel_sde", None),
     (Some(Mode::Std), "no_fp_fmt_parse", None),
     (Some(Mode::Std), "no_global_oom_handling", None),