Address some rustc inconsistency issues

We noticed when building rustc multiple time in a roll, some files
will not be consistent across the build despite the fact that they
are built from same source under the same environment. This patch
addresses the inconsistency issue we found on libunwind.a by sorting
the order of the files passed to the linker.

Author: zeroomega

src/bootstrap/src/core/build_steps/compile.rs

@@ -2376,15 +2376,19 @@ pub fn run_cargo(
     let mut deps = Vec::new();
     let mut toplevel = Vec::new();
     let ok = stream_cargo(builder, cargo, tail_args, &mut |msg| {
-        let (filenames, crate_types) = match msg {
+        let (filenames_vec, crate_types) = match msg {
             CargoMessage::CompilerArtifact {
                 filenames,
                 target: CargoTarget { crate_types },
                 ..
-            } => (filenames, crate_types),
+            } => {
+                let mut f: Vec<String> = filenames.into_iter().map(|s| s.into_owned()).collect();
+                f.sort(); // Sort the filenames
+                (f, crate_types)
+            }
             _ => return,
         };
-        for filename in filenames {
+        for filename in filenames_vec {
             // Skip files like executables
             let mut keep = false;
             if filename.ends_with(".lib")

src/bootstrap/src/core/build_steps/llvm.rs

@@ -1528,8 +1528,12 @@ impl Step for Libunwind {
 
         // FIXME: https://github.com/alexcrichton/cc-rs/issues/545#issuecomment-679242845
         let mut count = 0;
-        for entry in fs::read_dir(&out_dir).unwrap() {
-            let file = entry.unwrap().path().canonicalize().unwrap();
+        let mut files = fs::read_dir(&out_dir)
+            .unwrap()
+            .map(|entry| entry.unwrap().path().canonicalize().unwrap())
+            .collect::<Vec<_>>();
+        files.sort();
+        for file in files {
             if file.is_file() && file.extension() == Some(OsStr::new("o")) {
                 // Object file name without the hash prefix is "Unwind-EHABI", "Unwind-seh" or "libunwind".
                 let base_name = unhashed_basename(&file);