Clang update script: bump gnuwin version to include sort.exe

LLVM r347097 introduced a lit test that requires sort.

Bug: 904337
Change-Id: I2daaea742207a3b5a77a0b95571352928641c287
Reviewed-on: https://chromium-review.googlesource.com/c/1354939Reviewed-by: Nico Weber <thakis@chromium.org>
Commit-Queue: Hans Wennborg <hans@chromium.org>
Cr-Commit-Position: refs/heads/master@{#612202}

tools/clang/scripts/update.py

@@ -347,7 +347,7 @@ def AddGnuWinToPath():
     return
 
   gnuwin_dir = os.path.join(LLVM_BUILD_TOOLS_DIR, 'gnuwin')
-  GNUWIN_VERSION = '8'
+  GNUWIN_VERSION = '9'
   GNUWIN_STAMP = os.path.join(gnuwin_dir, 'stamp')
   if ReadStampFile(GNUWIN_STAMP) == GNUWIN_VERSION:
     print 'GNU Win tools already up to date.'