Revert of Change default Windows compiler to VS 2015

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 7248ed2479a87e950ccd7e93919fbaa704582796..1e20387b0b240e987b22e85898c9368d8b0b0b9a 100644
--- a/build/toolchain/win/setup_toolchain.py
+++ b/build/toolchain/win/setup_toolchain.py
@@ -156,18 +156,18 @@
           vc_bin_dir = os.path.realpath(path)
           break
 
-    # Add extra include directories here that need to be in front of the
-    # installed and packaged include directories. This may be needed in
-    # order to force a particular SDK version, such as to get VS 2013 to use
-    # the Windows 10 SDK. Beware of making the INCLUDE variable excessively
-    # long and be sure to make corresponding changes to build\common.gypi.
-    # Not currently used.
-    #if win_sdk_path:
-    #  additional_includes = [
-    #    os.path.join(win_sdk_path, 'Include', '10.0.10586.0', p)
-    #    for p in ['shared', 'um', 'winrt']]
-    #  additional_includes = os.path.pathsep.join(additional_includes)
-    #  env['INCLUDE'] = additional_includes + os.path.pathsep + env['INCLUDE']
+    # 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.
+    # Having the Windows SDK first is also the only way to control which SDK
+    # version is used.
+
+    if win_sdk_path:
+      additional_includes = [
+        os.path.join(win_sdk_path, 'Include', '10.0.10586.0', p)
+        for p in ['shared', 'um', 'winrt']]
+      additional_includes = os.path.pathsep.join(additional_includes)
+      env['INCLUDE'] = additional_includes + os.path.pathsep + env['INCLUDE']
     env_block = _FormatAsEnvironmentBlock(env)
     with open('environment.' + cpu, 'wb') as f:
       f.write(env_block)