Revert "Use urllib instead of curl"

This reverts commit fd6e6ffb.

Reason for revert: https://crbug.com/1067752

Original change's description:
> Use urllib instead of curl
> 
> Now that https://crbug.com/965937 is fixed.
> Partial revert of https://crrev.com/c/1624331.
> 
> Change-Id: I9e73fdff99984601182ec142723a9d3521a9eb6e
> Bug: 897796
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2134702
> Commit-Queue: Arthur Eubanks <aeubanks@google.com>
> Auto-Submit: Arthur Eubanks <aeubanks@google.com>
> Reviewed-by: Hans Wennborg <hans@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#756285}

TBR=hans@chromium.org,aeubanks@google.com

Change-Id: Ia53d6e84a8e09d13d7935cfde3b9310d7bc06e93
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 897796
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2136138Reviewed-by: Nico Weber <thakis@chromium.org>
Commit-Queue: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#756434}

tools/clang/scripts/build.py

@@ -22,14 +22,6 @@ import shutil
 import subprocess
 import sys
 
-
-try:
-  import urllib2 as urllib
-except ImportError:  # For Py3 compatibility
-  import urllib.request as urllib
-  import urllib.error as urllib
-
-
 from update import (CDS_URL, CHROMIUM_DIR, CLANG_REVISION, LLVM_BUILD_DIR,
                     FORCE_HEAD_REVISION_FILE, PACKAGE_VERSION, RELEASE_VERSION,
                     STAMP_FILE, CopyFile, CopyDiaDllTo, DownloadUrl,
@@ -136,12 +128,19 @@ def CheckoutLLVM(commit, dir):
   sys.exit(1)
 
 
+def UrlOpen(url):
+  # Normally we'd use urllib, but on our bots it can't connect to the GitHub API
+  # due to using too old TLS (see crbug.com/897796#c56). As a horrible
+  # workaround, shell out to curl instead. It seems curl is recent enough on all
+  # our machines that it can connect. On Windows it's in our gnuwin package.
+  # TODO(crbug.com/965937): Use urllib once our Python is recent enough.
+  return subprocess.check_output(['curl', '--silent', url])
+
 
 def GetLatestLLVMCommit():
   """Get the latest commit hash in the LLVM monorepo."""
-  ref = json.loads(
-      urllib.urlopen(('https://api.github.com/repos/'
-                      'llvm/llvm-project/git/refs/heads/master')).read())
+  ref = json.loads(UrlOpen(('https://api.github.com/repos/'
+                            'llvm/llvm-project/git/refs/heads/master')))
   assert ref['object']['type'] == 'commit'
   return ref['object']['sha']
 
@@ -395,6 +394,12 @@ def main():
   # Don't buffer stdout, so that print statements are immediately flushed.
   sys.stdout = os.fdopen(sys.stdout.fileno(), 'w', 0)
 
+  # The gnuwin package also includes curl, which is needed to interact with the
+  # github API below.
+  # TODO(crbug.com/965937): Use urllib once our Python is recent enough, and
+  # move this down to where we fetch other build tools.
+  AddGnuWinToPath()
+
   # TODO(crbug.com/929645): Remove once we build on host systems with a modern
   # enough GCC to build Clang.
   MaybeDownloadHostGcc(args)
@@ -415,7 +420,6 @@ def main():
   WriteStampFile('', FORCE_HEAD_REVISION_FILE)
 
   AddCMakeToPath(args)
-  AddGnuWinToPath()
   DeleteChromeToolsShim()