Fix gn builds with locally installed VS

build/toolchain/win/setup_toolchain.py

Index: build/toolchain/win/setup_toolchain.py
diff --git a/build/toolchain/win/setup_toolchain.py b/build/toolchain/win/setup_toolchain.py
index d2dc4609644fe9862901e8938b8c590bc54eace0..ae3d28932293c5d85170f5f688a1ef590ca5481c 100644
--- a/build/toolchain/win/setup_toolchain.py
+++ b/build/toolchain/win/setup_toolchain.py
@@ -153,11 +153,16 @@ def main():
     # The Windows SDK include directories must be first. They both have a sal.h,
     # and the SDK one is newer and the SDK uses some newer features from it not
     # present in the Visual Studio one.
+    # I suspect this is not true in the brave-new world of VS 2015. However
+    # when building with an installed version of VS 2013 there are additional
+    # reasons to put these first - it's the only way to get the Windows 10
+    # SDK to be used.
 
     if win_sdk_path:
-      additional_includes = ('{sdk_dir}\\Include\\shared;' +
-                             '{sdk_dir}\\Include\\um;' +
-                             '{sdk_dir}\\Include\\winrt;').format(
+      # In package_from_installed.py this goes um;shared;winrt;ucrt
+      additional_includes = ('{sdk_dir}\\Include\\10.0.10586.0\\shared;' +
+                             '{sdk_dir}\\Include\\10.0.10586.0\\um;' +
+                             '{sdk_dir}\\Include\\10.0.10586.0\\winrt;').format(
                                   sdk_dir=win_sdk_path)
       env['INCLUDE'] = additional_includes + env['INCLUDE']
     env_block = _FormatAsEnvironmentBlock(env)