--- rustc-1.38.0-src/src/bootstrap/builder.rs	2019-09-23 14:15:52.000000000 -0700
+++ rustc-1.38.0-src/src/bootstrap/builder.rs	2019-09-26 10:45:49.663995011 -0700
@@ -140,6 +140,7 @@
 
 impl StepDescription {
     fn from<S: Step>() -> StepDescription {
+        #[allow(unused_unsafe)] // for rebuild bootstrapping
         StepDescription {
             default: S::DEFAULT,
             only_hosts: S::ONLY_HOSTS,