Revert of clang/win update.py: Put gnuwin last in path. (patchset Pis…

…sandshittium#1 id:1 of https://codereview.chromium.org/1887163003/ )

Reason for revert:
Didn't help: Cygwin is in the PATH when ssh'ing in, but not for normal build steps on the bot.

Original issue's description:
> clang/win update.py: Put gnuwin last in path.
>
> gnuwin's rm.exe doesn't seem to work with long path names on the bots for some
> reason.  The bots have cygwin installed and have a better working rm.exe
> earlier in the path, so try to use this.  (Local devs don't have long paths.)
>
> BUG=603364
> NOTRY=true
>
> Committed: https://crrev.com/051cfcb6697da79bd57d47e923505d2ec806cc3a
> Cr-Commit-Position: refs/heads/master@{#387463}

TBR=hans@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=603364

Review URL: https://codereview.chromium.org/1888353003

Cr-Commit-Position: refs/heads/master@{#387595}

tools/clang/scripts/update.py

@@ -333,7 +333,7 @@ def AddGnuWinToPath():
     DownloadAndUnpack(CDS_URL + '/tools/' + zip_name, LLVM_BUILD_TOOLS_DIR)
     WriteStampFile(GNUWIN_VERSION, GNUWIN_STAMP)
 
-  os.environ['PATH'] = os.environ.get('PATH', '') + os.pathsep + gnuwin_dir
+  os.environ['PATH'] = gnuwin_dir + os.pathsep + os.environ.get('PATH', '')
 
 
 vs_version = None