Update highest shader model to 6.6 in execution tests (#3083)

tools/clang/unittests/HLSL/ExecutionTest.cpp

@@ -484,6 +484,7 @@ public:
     D3D_SHADER_MODEL_6_3 = 0x63,
     D3D_SHADER_MODEL_6_4 = 0x64,
     D3D_SHADER_MODEL_6_5 = 0x65,
+    D3D_SHADER_MODEL_6_6 = 0x66,
 } D3D_SHADER_MODEL;
 
 #if WDK_NTDDI_VERSION == NTDDI_WIN10_RS2
@@ -500,8 +501,10 @@ public:
   static const D3D_SHADER_MODEL HIGHEST_SHADER_MODEL = D3D_SHADER_MODEL_6_5;
 #elif WDK_NTDDI_VERSION == NTDDI_WIN10_MN
   static const D3D_SHADER_MODEL HIGHEST_SHADER_MODEL = D3D_SHADER_MODEL_6_5;
+#elif WDK_NTDDI_VERSION == NTDDI_WIN10_FE
+  static const D3D_SHADER_MODEL HIGHEST_SHADER_MODEL = D3D_SHADER_MODEL_6_6;
 #else
-  static const D3D_SHADER_MODEL HIGHEST_SHADER_MODEL = D3D_SHADER_MODEL_6_5;
+  static const D3D_SHADER_MODEL HIGHEST_SHADER_MODEL = D3D_SHADER_MODEL_6_6;
 #endif
 
   bool UseDxbc() {