Make Clang's update.py use the Win toolchain under depot_tools if available

DEPS

Index: DEPS
diff --git a/DEPS b/DEPS
index 18422d459dc149d43d4dbc182836c7ce6bd05144..e6ec931b022e5bd21417e8a64600b6dfbd805035 100644
--- a/DEPS
+++ b/DEPS
@@ -596,18 +596,19 @@ hooks = [
         '--arch=i386'],
   },
   {
-    # Pull clang if on Mac or clang is requested via GYP_DEFINES.
-    'name': 'clang',
-    'pattern': '.',
-    'action': ['python', 'src/tools/clang/scripts/update.py', '--if-needed'],
-  },
-  {
     # Update the Windows toolchain if necessary.
     'name': 'win_toolchain',
     'pattern': '.',
     'action': ['python', 'src/build/vs_toolchain.py', 'update'],
   },
   {
+    # Pull clang if needed or requested via GYP_DEFINES.
+    # Note: On Win, this should run after win_toolchain, as it may use it.
+    'name': 'clang',
+    'pattern': '.',
+    'action': ['python', 'src/tools/clang/scripts/update.py', '--if-needed'],
+  },
+  {
     # Update LASTCHANGE. This is also run by export_tarball.py in
     # src/tools/export_tarball - please keep them in sync.
     'name': 'lastchange',