add -Iinclude/private anywhere we have -Isrc/core

gyp/core.gyp

 # Copyright 2015 Google Inc.
 #
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 # Core Skia library code.
 {
   'targets': [
     {
       'target_name': 'core',
       'product_name': 'skia_core',
       'type': 'static_library',
       'standalone_static_library': 1,
       'msvs_guid': 'B7760B5E-BFA8-486B-ACFD-49E3A6DE8E76',
 
       'includes': [
         'core.gypi',
       ],
 
       'include_dirs': [
         '../include/c',
         '../include/config',
         '../include/core',
         '../include/pathops',
         '../include/pipe',
         '../include/ports',
+        '../include/private',
         '../include/utils',
         '../include/images',
         '../src/core',
         '../src/sfnt',
         '../src/image',
         '../src/opts',
         '../src/utils',
       ],
       'sources': [
         'core.gypi', # Makes the gypi appear in IDEs (but does not modify the build).
@@ skipping 87 matching lines @@
           [ 'skia_os == "win"', {
             'include_dirs': [
               'config/win',
             ],
           }],
         ],
       },
     },
   ],
 }