Reland "Clang update.py: Don't set mtime based on the archive metadata"

This is a reland of commit 9a05872,
adding follow_symlinks=False to the utime() call to avoid failing
if the extracted archive contains broken symlinks, as seems to be the
case on Mac.

I think it makes sense not to follow symlinks here anyway: we want to
set the mtime on the link itself. If the target is in the archive,
it will get set separately.

Original change's description:
> Clang update.py: Don't set mtime based on the archive metadata
>
> We want the extracted files to have mtimes that reflect when they
> were extracted.
>
> The build system relies on mtimes information to detect when
> dependencies change.
>
> Since we want update.py to work with system python on macOS (3.9.6),
> we can't use the extractall filter mechanism, but instead update
> the mtimes ourselves.
>
> Bug: 450551220
> Change-Id: Ie6baa486520e85e0e48106c5ea43bd844baa3cb1
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7046440
> Reviewed-by: Nico Weber <[email protected]>
> Commit-Queue: Hans Wennborg <[email protected]>
> Cr-Commit-Position: refs/heads/main@{#1531327}

Bug: 450551220
Change-Id: Ib0d2246be5cb9dd30921deb57ddb2f403abea8ca
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7062434
Auto-Submit: Hans Wennborg <[email protected]>
Reviewed-by: Nico Weber <[email protected]>
Commit-Queue: Hans Wennborg <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1532375}

Author: zmodem

tools/clang/scripts/update.py

@@ -191,12 +191,18 @@ def DownloadAndUnpack(url, output_dir, path_prefixes=None, is_known_zip=False):
       zipfile.ZipFile(f).extractall(path=output_dir)
     else:
       t = tarfile.open(mode='r:*', fileobj=f)
-      members = None
+      members = t.getmembers()
       if path_prefixes is not None:
         members = [m for m in t.getmembers()
                    if any(m.name.startswith(p) for p in path_prefixes)]
       t.extractall(path=output_dir, members=members)
 
+      # Don't set mtime based on the archive metadata; see crbug.com/450551220
+      # The nicest way to do this would be by passing a filter to extractall,
+      # but that functionality is not available in macOS system Python (3.9.6).
+      for m in members:
+        os.utime(os.path.join(output_dir, m.name), follow_symlinks=False)
+
 
 def GetPlatformUrlPrefix(host_os):
   _HOST_OS_URL_MAP = {