Build C code with LTO when LTO is enabled for rust code

Author: bjorn3

src/bootstrap/src/utils/cc_detect.rs

@@ -25,7 +25,7 @@ use std::collections::HashSet;
 use std::iter;
 use std::path::{Path, PathBuf};
 
-use crate::core::config::TargetSelection;
+use crate::core::config::{RustcLto, TargetSelection};
 use crate::utils::exec::{BootstrapCommand, command};
 use crate::{Build, CLang, GitRepo};
 
@@ -53,6 +53,15 @@ fn new_cc_build(build: &Build, target: TargetSelection) -> cc::Build {
             }
         }
     }
+    match build.config.rust_lto {
+        RustcLto::Off | RustcLto::ThinLocal => {}
+        RustcLto::Thin => {
+            cfg.flag_if_supported("-flto=thin");
+        }
+        RustcLto::Fat => {
+            cfg.flag_if_supported("-flto=full");
+        }
+    }
     cfg
 }