record mtime in llvm linker script

This will avoid rebuilds due to the script being more recent than the
rest of the original files.

src/bootstrap/src/core/build_steps/dist.rs

@@ -2048,6 +2048,13 @@ fn install_llvm_file(
             let link = t!(fs::read_link(source));
             let mut linker_script = t!(fs::File::create(full_dest));
             t!(write!(linker_script, "INPUT({})\n", link.display()));
+
+            // We also want the linker script to have the same mtime as the source, otherwise it
+            // can trigger rebuilds.
+            let meta = t!(fs::metadata(source));
+            if let Ok(mtime) = meta.modified() {
+                t!(linker_script.set_modified(mtime));
+            }
         }
     } else {
         builder.install(&source, destination, 0o644);