Auto merge of #78790 - Gankra:rust-src-vendor, r=Mark-Simulacrum

Vendor libtest's dependencies in the rust-src component

This is the Rust side of https://github.com/rust-lang/wg-cargo-std-aware/issues/23

Note that this won't produce a useful result for `cargo -Zbuild-std` if there are multiple versions of a crate vendored, but will otherwise produce a valid vendor dir.

See https://github.com/rust-lang/cargo/pull/8834 for the other half of this change.

src/bootstrap/lib.rs

@@ -1171,6 +1171,27 @@ impl Build {
         paths
     }
 
+    /// Copies a file from `src` to `dst` and doesn't use links, so
+    /// that the copy can be modified without affecting the original.
+    pub fn really_copy(&self, src: &Path, dst: &Path) {
+        if self.config.dry_run {
+            return;
+        }
+        self.verbose_than(1, &format!("Copy {:?} to {:?}", src, dst));
+        if src == dst {
+            return;
+        }
+        let _ = fs::remove_file(&dst);
+        let metadata = t!(src.symlink_metadata());
+        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()));
+        let atime = FileTime::from_last_access_time(&metadata);
+        let mtime = FileTime::from_last_modification_time(&metadata);
+        t!(filetime::set_file_times(dst, atime, mtime));
+    }
+
     /// Copies a file from `src` to `dst`
     pub fn copy(&self, src: &Path, dst: &Path) {
         if self.config.dry_run {