Move uils and sksl to a common sources GYP file.

gyp/skslc.gyp

 # Copyright 2016 Google Inc.
 #
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 {
   'includes': [
     'apptype_console.gypi',
   ],
+  'variables': {
+    'includes': [ 'skia_sources.gypi' ],
+  },
   'targets': [
     {
       'target_name': 'skslc',
       'type': 'executable',
-      'includes' : [
-        'sksl.gypi',
-      ],
+      'include_dirs': [ '<@(sksl_include_dirs)' ],
       'sources': [
+        '<@(sksl_sources)',
         '../src/sksl/SkSLMain.cpp',
       ],
       'configurations': {
         'Debug': {
           'defines': [
             'DEBUG',
           ],
         },
       },
     },
   ],
 }