[libcxx] Preserve order, avoid duplicates when merging static archives

[phosek]

Summary

glob can return files in arbitrary order which breaks deterministic
builds. Rather, use ar t to list the files in each archive and
preserve the original order. Using ar q results in duplicate entries
in the archive, instead use ar r to avoid duplicates.

utils/merge_archives.py

if exitCode != 0 or verbose:
             report += "Standard Output:\n--\n%s--" % out
         if err:
             report += "Standard Error:\n--\n%s--" % err
         if exitCode != 0:
             report += "\n\nFailed!"
         sys.stderr.write('%s\n' % report)
         if exitCode != 0:
             exit_with_cleanups(exitCode)
+    return out
 
 def main():
     parser = ArgumentParser(
         description="Merge multiple archives into a single library")
     parser.add_argument(
         '-v', '--verbose', dest='verbose', action='store_true', default=False)
     parser.add_argument(
         '-o', '--output', dest='output', required=True,
archives = [find_and_diagnose_missing(ar, args.search_paths)
                 for ar in args.archives]
     print ('Merging archives: %s' % archives)
     if not os.path.exists(os.path.dirname(args.output)):
         print_and_exit("output path doesn't exist: '%s'" % args.output)
 
     global temp_directory_root
     temp_directory_root = tempfile.mkdtemp('.libcxx.merge.archives')
 
+    files = []
     for arc in archives:
-        execute_command_verbose([ar_exe, 'x', arc], cwd=temp_directory_root,
-                                verbose=args.verbose)
+        execute_command_verbose([ar_exe, 'x', arc],
+                                cwd=temp_directory_root, verbose=args.verbose)
+        out = execute_command_verbose([ar_exe, 't', arc])
+        files.extend(out.splitlines())
 
-    files = glob.glob(os.path.join(temp_directory_root, '*.o*'))
-    if not files:
-        print_and_exit('Failed to glob for %s' % temp_directory_root)
-    cmd = [ar_exe, 'qcs', args.output] + files
-    execute_command_verbose(cmd, cwd=temp_directory_root, verbose=args.verbose)
+    execute_command_verbose([ar_exe, 'rcsD', args.output] + files,
+                            cwd=temp_directory_root, verbose=args.verbose)
 
 
 if __name__ == '__main__':
     main()
     exit_with_cleanups(0)