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

gyp/shaderc.gyp

Index: gyp/shaderc.gyp
diff --git a/gyp/shaderc.gyp b/gyp/shaderc.gyp
index 26af80a4d1e19f5f0613dc214bd7c21c368f19ad..7732e221ac049547005717b29367c9b6fa563df1 100644
--- a/gyp/shaderc.gyp
+++ b/gyp/shaderc.gyp
@@ -8,12 +8,8 @@
   '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',
         }, {