Fix bootstrap on Windows

patches/fix_bootstrap_windows.patch

@@ -0,0 +1,77 @@
+diff --git a/src/bootstrap/src/core/download.rs b/src/bootstrap/src/core/download.rs
+index 56a8528d..b8e862da 100644
+--- a/src/bootstrap/src/core/download.rs
++++ b/src/bootstrap/src/core/download.rs
+@@ -706,9 +706,7 @@ pub(crate) fn maybe_download_ci_llvm(&self) {
+             let file_times = fs::FileTimes::new().set_accessed(now).set_modified(now);
+
+             let llvm_config = llvm_root.join("bin").join(exe("llvm-config", self.build));
+-            let llvm_config_file = t!(File::options().write(true).open(llvm_config));
+-
+-            t!(llvm_config_file.set_times(file_times));
++            t!(crate::utils::helpers::set_file_times(llvm_config, file_times));
+
+             if self.should_fix_bins_and_dylibs() {
+                 let llvm_lib = llvm_root.join("lib");
+diff --git a/src/bootstrap/src/lib.rs b/src/bootstrap/src/lib.rs
+index a8555b2c..7b55463a 100644
+--- a/src/bootstrap/src/lib.rs
++++ b/src/bootstrap/src/lib.rs
+@@ -41,7 +41,9 @@
+ use crate::core::config::{DryRun, Target};
+ use crate::core::config::{LlvmLibunwind, TargetSelection};
+ use crate::utils::exec::{command, BehaviorOnFailure, BootstrapCommand, CommandOutput};
+-use crate::utils::helpers::{self, dir_is_empty, exe, libdir, mtime, output, symlink_dir};
++use crate::utils::helpers::{
++    self, dir_is_empty, exe, libdir, mtime, output, set_file_times, symlink_dir,
++};
+
+ mod core;
+ mod utils;
+@@ -1725,21 +1727,20 @@ fn copy_link_internal(&self, src: &Path, dst: &Path, dereference_symlinks: bool)
+             }
+         }
+         if let Ok(()) = fs::hard_link(&src, dst) {
+-            // Attempt to "easy copy" by creating a hard link
+-            // (symlinks don't work on windows), but if that fails
+-            // just fall back to a slow `copy` operation.
++            // Attempt to "easy copy" by creating a hard link (symlinks are priviledged on windows),
++            // but if that fails just fall back to a slow `copy` operation.
+         } else {
+             if let Err(e) = fs::copy(&src, dst) {
+                 panic!("failed to copy `{}` to `{}`: {}", src.display(), dst.display(), e)
+             }
+             t!(fs::set_permissions(dst, metadata.permissions()));
+
++            // Restore file times because changing permissions on e.g. Linux using `chmod` can cause
++            // file access time to change.
+             let file_times = fs::FileTimes::new()
+                 .set_accessed(t!(metadata.accessed()))
+                 .set_modified(t!(metadata.modified()));
+-
+-            let dst_file = t!(fs::File::open(dst));
+-            t!(dst_file.set_times(file_times));
++            t!(set_file_times(dst, file_times));
+         }
+     }
+
+diff --git a/src/bootstrap/src/utils/helpers.rs b/src/bootstrap/src/utils/helpers.rs
+index 773a873e..72ec05e6 100644
+--- a/src/bootstrap/src/utils/helpers.rs
++++ b/src/bootstrap/src/utils/helpers.rs
+@@ -545,3 +545,15 @@ pub fn get_closest_merge_base_commit(
+
+     Ok(output_result(git.as_command_mut())?.trim().to_owned())
+ }
++
++/// Sets the file times for a given file at `path`.
++pub fn set_file_times<P: AsRef<Path>>(path: P, times: fs::FileTimes) -> io::Result<()> {
++    // Windows requires file to be writable to modify file times. But on Linux CI the file does not
++    // need to be writable to modify file times and might be read-only.
++    let f = if cfg!(windows) {
++        fs::File::options().write(true).open(path)?
++    } else {
++        fs::File::open(path)?
++    };
++    f.set_times(times)
++}