Make two compilation flags for Windows Clang build effective

build_gyp/standalone.gypi

Index: build_gyp/standalone.gypi
diff --git a/build_gyp/standalone.gypi b/build_gyp/standalone.gypi
index 250c085e1896e75f678d7f79d3e0db00483efbf0..f7cad6622a76bd921bdbd66882287016d220a81b 100644
--- a/build_gyp/standalone.gypi
+++ b/build_gyp/standalone.gypi
@@ -339,18 +339,14 @@
             ],
           }],
           ['OS=="win" and clang==1 and MSVS_VERSION == "2013"', {
-            'VCCLCompilerTool': {
-              'AdditionalOptions': [
-                '-fmsc-version=1800',
-              ],
-            },
+            'AdditionalOptions': [
+              '-fmsc-version=1800',
+            ],
           }],
           ['OS=="win" and clang==1 and MSVS_VERSION == "2015"', {
-            'VCCLCompilerTool': {
-              'AdditionalOptions': [
-                '-fmsc-version=1900',
-              ],
-            },
+            'AdditionalOptions': [
+              '-fmsc-version=1900',
+            ],
           }],
         ],
       },