Add script for updating node and python binaries in google storage (#486)

In both cases updating these is slightly non-trivial so encode
the process in the script.

scripts/update_node.py

@@ -0,0 +1,51 @@
+#!/usr/bin/env python3
+# Copyright 2020 The Emscripten Authors.  All rights reserved.
+# Emscripten is available under two separate licenses, the MIT license and the
+# University of Illinois/NCSA Open Source License.  Both these licenses can be
+# found in the LICENSE file.
+
+"""Updates the node binaries that we cache store at
+http://storage.google.com/webassembly.
+
+For the windows version we also alter the directory layout to add the 'bin'
+direcotry.
+"""
+
+import urllib.request
+import subprocess
+import os
+import shutil
+
+version = '12.16.3'
+base = 'https://nodejs.org/dist/latest-v12.x/'
+upload_base = 'gs://webassembly/emscripten-releases-builds/deps/'
+
+suffixes = [
+    '-win-x64.zip',
+    '-darwin-x64.tar.gz',
+    '-linux-x64.tar.xz',
+    '-linux-arm64.tar.xz',
+    '-linux-armv7l.tar.xz',
+]
+
+for suffix in suffixes:
+    filename = 'node-v%s%s' % (version, suffix)
+    download_url = base + filename
+    print('Downloading: ' + download_url)
+    urllib.request.urlretrieve(download_url, filename)
+
+    if '-win-' in suffix:
+      subprocess.check_call(['unzip', '-q', filename])
+      dirname = os.path.splitext(os.path.basename(filename))[0]
+      shutil.move(dirname, 'bin')
+      os.mkdir(dirname)
+      shutil.move('bin', dirname)
+      subprocess.check_call(['zip', '-rq', filename, dirname])
+      shutil.rmtree(dirname)
+
+    upload_url = upload_base + filename
+    print('Uploading: ' + upload_url)
+    cmd = ['gsutil', 'cp', '-n', filename, upload_url]
+    print(' '.join(cmd))
+    subprocess.check_call(cmd)
+    os.remove(filename)