automate-git: Windows: Patch VS toolchain scripts before runhooks

Split `gclient sync` into separate `gclient sync --nohooks` and
`gclient runhooks` steps so that we can optionally apply patches
from `runhooks.patch` in-between. This is necessary because the
src/tools/clang/scripts/update.py script is run via a hook and has
dependencies on the VS toolchain scripts which must be patched to
properly consider the GYP_MSVS_VERSION environment variable.

patch/patch.cfg

@@ -26,9 +26,6 @@ patches = [
     # Move chrome target locales output to a chrome/ directory to avoid
     # conflicts with the CEF configuration.
     #
-    # Support custom VS toolchain on Windows.
-    # https://bugs.chromium.org/p/chromium/issues/detail?id=623342
-    #
     # Write environment.* files with the correct SDK version on Windows.
     # https://bugs.chromium.org/p/chromium/issues/detail?id=634788
     #
@@ -36,6 +33,14 @@ patches = [
     # https://bitbucket.org/chromiumembedded/cef/issues/2432
     'name': 'gn_config',
   },
+  {
+    # Patches that must be applied after `gclient sync --nohooks` and before
+    # `gclient runhooks`.
+    #
+    # Support custom VS toolchain on Windows.
+    # https://bugs.chromium.org/p/chromium/issues/detail?id=623342
+    'name': 'runhooks',
+  },
   {
     # Support component builds (GN is_component_build=true).
     # https://bitbucket.org/chromiumembedded/cef/issues/1617