Make build_shaderc.py blow away output dir and allow build_type arg to contain either Debug or Relea

gyp/shaderc.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.
 
 # Builds shaderc for the Vulkan backend
 {
   'variables': {
     'variables': { # This is the dreaded nested variables dict so that we can
                    # have dependent variables
+      'shaderc_build_configuration': '<(CONFIGURATION_NAME)',
       'conditions': [
-        [ 'CONFIGURATION_NAME == "Release_Developer"', {
-          'shaderc_build_configuration' : 'Release',
-        }, {
-          'shaderc_build_configuration' : '<(CONFIGURATION_NAME)',
-        }],
         [ 'skia_os == "win"', {
           'shaderc_lib_name' : 'shaderc_combined.lib',
         }, {
           'shaderc_lib_name' : 'libshaderc_combined.a',
         }],
         [ 'skia_os == "win"', {
           'conditions': [
             [ 'MSVS_VERSION == "2013"', {
               'shaderc_project_type' : 'MSVS2013',
             }],
@@ skipping 51 matching lines @@
       'all_dependent_settings': {
         'link_settings': {
           'libraries': [
             '<(shaderc_lib_name)',
           ],
         },
       },
     },
   ],
 }