clang tot bots: Don't depend on svn.exe from depot_tools.

tools/clang/scripts/update.py

Index: tools/clang/scripts/update.py
diff --git a/tools/clang/scripts/update.py b/tools/clang/scripts/update.py
index 473a43b588d29065fcd80c5f531291041003bc2e..7cf810efe1966d9e89e5ed39e66bd93901861221 100755
--- a/tools/clang/scripts/update.py
+++ b/tools/clang/scripts/update.py
@@ -312,6 +312,17 @@ def DownloadHostGcc(args):
   args.gcc_toolchain = gcc_dir
 
 
+def AddSvnToPathOnWin():
+  """Download svn.exe and add it to PATH."""
+  if sys.platform != 'win32':
+    return
+  svn_ver = 'svn-1.6.6-win'
+  svn_dir = os.path.join(LLVM_BUILD_TOOLS_DIR, svn_ver)
+  if not os.path.exists(svn_dir):
+    DownloadAndUnpack(CDS_URL + '/tools/%s.zip' % svn_ver, LLVM_BUILD_TOOLS_DIR)
+  os.environ['PATH'] = svn_dir + os.pathsep + os.environ.get('PATH', '')
+
+
 def AddCMakeToPath():
   """Download CMake and add it to PATH."""
   if sys.platform == 'win32':
@@ -448,6 +459,7 @@ def UpdateClang(args):
     return 1
 
   DownloadHostGcc(args)
+  AddSvnToPathOnWin()
   AddCMakeToPath()
   AddGnuWinToPath()