Try building rustc with codegen-units=5

Author: tmiasko

src/bootstrap/builder.rs

@@ -1444,7 +1444,10 @@ impl<'a> Builder<'a> {
         }
 
         match (mode, self.config.rust_codegen_units_std, self.config.rust_codegen_units) {
-            (Mode::Std, Some(n), _) | (_, _, Some(n)) => {
+            (Mode::Rustc, _, Some(n)) => {
+                cargo.env(profile_var("CODEGEN_UNITS"), n.to_string());
+            }
+            (Mode::Std, Some(n), _) => {
                 cargo.env(profile_var("CODEGEN_UNITS"), n.to_string());
             }
             _ => {

src/ci/run.sh

@@ -52,6 +52,7 @@ RUST_CONFIGURE_ARGS="$RUST_CONFIGURE_ARGS --disable-manage-submodules"
 RUST_CONFIGURE_ARGS="$RUST_CONFIGURE_ARGS --enable-locked-deps"
 RUST_CONFIGURE_ARGS="$RUST_CONFIGURE_ARGS --enable-cargo-native-static"
 RUST_CONFIGURE_ARGS="$RUST_CONFIGURE_ARGS --set rust.codegen-units-std=1"
+RUST_CONFIGURE_ARGS="$RUST_CONFIGURE_ARGS --set rust.codegen-units=5"
 
 # Only produce xz tarballs on CI. gz tarballs will be generated by the release
 # process by recompressing the existing xz ones. This decreases the storage