fix dotnet not found

Author: artidoro

src/Directory.Build.props

@@ -24,6 +24,7 @@
 <!-- API Compat -->
   <PropertyGroup>
     <RunApiCompat Condition="'$(RunApiCompat)' == ''">$(IsStableProject)</RunApiCompat>
+    <ToolHostCmd Condition="'$(ToolHostCmd)'==''">$(ToolsDir)dotnetcli/dotnet.exe</ToolHostCmd>
 
     <!-- only validate that the current implementation is compatible
          with the old one, not vice-versa (since latest may have new