[tools][fuchsia] Do not tar debug symbol CIPD uploads (flutter#17506)

Fuchsia is the main consumer of these CIPD packages and - to simplify
its infrastructure - it is migrating its SDK partners over to producing
a CIPD package containing a flat .build-id directory.

This change also updates the CIPD package so that the .build-id
directory is placed at the root.

Bug: fxbug.dev/41443

tools/fuchsia/merge_and_upload_debug_symbols.py

@@ -73,16 +73,22 @@ def ProcessCIPDPackage(upload, cipd_yaml, engine_version, out_dir, target_arch):
       if tries == num_tries - 1:
         raise
 
-def CreateTarFile(folder_path, base_dir):
-  archive_name = os.path.basename(folder_path)
-  tar_file_path = os.path.join(base_dir, archive_name + '.tar.bz2')
-  with tarfile.open(tar_file_path, "w:bz2") as archive:
-    for root, dirs, _ in os.walk(folder_path):
-      for dir_name in dirs:
-        dir_path = os.path.join(root, dir_name)
-        archive.add(dir_path, arcname=dir_name)
-  return tar_file_path
-
+# Recursively hardlinks contents from one directory to another,
+# skipping over collisions.
+def HardlinkContents(dirA, dirB):
+  for src_dir, _, filenames in os.walk(dirA):
+    for filename in filenames:
+      src = os.path.join(src_dir, filename)
+      dest_dir = os.path.join(dirB, os.path.relpath(src_dir, dirA))
+      os.makedirs(dest_dir,  exist_ok=True)
+      dest = os.path.join(dest_dir, filename)
+      if os.path.exists(dest):
+        # The last two path components provide a content address for a .build-id entry.
+        tokens = os.path.split(dest)
+        name = os.path.join(tokens[-2], tokens[-1])
+        print('%s already exists in destination; skipping linking' % name)
+        continue
+      os.link(src, dest)
 
 def main():
   parser = argparse.ArgumentParser()
@@ -114,18 +120,17 @@ def main():
   for symbol_dir in symbol_dirs:
     assert os.path.exists(symbol_dir) and os.path.isdir(symbol_dir)
 
-  arch = args.target_arch
-  out_dir = os.path.join(args.out_dir,
-                         'flutter-fuchsia-debug-symbols-%s' % arch)
+  out_dir = args.out_dir
+
   if os.path.exists(out_dir):
     print 'Directory: %s is not empty, deleting it.' % out_dir
     shutil.rmtree(out_dir)
   os.makedirs(out_dir)
 
   for symbol_dir in symbol_dirs:
-    archive_path = CreateTarFile(symbol_dir, out_dir)
-    print('Created archive: ' + archive_path)
+    HardlinkContents(symbol_dir, out_dir)
 
+  arch = args.target_arch
   cipd_def = WriteCIPDDefinition(arch, out_dir)
   ProcessCIPDPackage(args.upload, cipd_def, args.engine_version, out_dir, arch)
   return 0