title: Nuke Build declare a tool that is fetched as part of the build
body: <p>Most of the tools I use, are dotnet tools that are referenced from csproj file and automagically fetched by nuget.
  A few tools are old-school Framework tools, which should be copied into the tools directory before use.
  For the latter I have a GetTools Target.</p>
  <p>My problem is declaring the Tool:</p>
  <pre><code> [LocalExecutable(&quot;./tools/MyFrameworkTool.exe&quot;)] 
   readonly Tool FrameworkTool;
  </code></pre>
  <p>This throws the following assertion:</p>
  <pre><code>Assertion failed: File.Exists(C:\Jenkins\workspace\Job\./tools/MyFrameworkTool.exe)
  </code></pre>
  <p>And the FrameworkTool is null.</p>
  <p>How can I make a 'late' declaration of the tool, when it has been fetched by the GetTools Target?</p>