Adding missing v120 winrt test runner to dirs.proj.

Author: stgates

Release/tests/common/TestRunner/dirs.proj

@@ -5,6 +5,10 @@
   <ItemGroup Condition="'$(DevToolsVersion)'=='120'">
       <ProjectFile Include="VS12\TestRunner120.vcxproj" />
   </ItemGroup>
+  
+  <ItemGroup Condition="'$(OsVersion)|$(DevToolsVersion)'=='6.3|120'">
+  	<ProjectFile Include="vs12.winrt\TestRunner120.winrt.vcxproj" />
+  </ItemGroup>
 
   <ItemGroup Condition="'$(DevToolsVersion)'=='140'">
     <ProjectFile Include="VS14\TestRunner140.vcxproj" />