added initial GLSL support to skslc

gyp/sksl.gypi

 # Copyright 2016 Google Inc.
 #
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 {
   'include_dirs': [
     '../include',
     '../include/config',
     '../include/core',
     '../include/private',
     '../src/sksl',
   ],
   'sources': [
     '../src/sksl/SkSLCompiler.cpp',
     '../src/sksl/SkSLIRGenerator.cpp',
     '../src/sksl/SkSLParser.cpp',
+    '../src/sksl/SkSLGLSLCodeGenerator.cpp',
     '../src/sksl/SkSLSPIRVCodeGenerator.cpp',
     '../src/sksl/SkSLUtil.cpp',
     '../src/sksl/ir/SkSLSymbolTable.cpp',
     '../src/sksl/ir/SkSLType.cpp',
   ],
 }