Add macro that contains current targets

I would like to create a target inside my project using the BeforeTargets attribute that builds a dependency with another call to MSBuild, and I want to pass the same target(s) to the new invocation that will run after the BeforeTargets finishes using a marcro.

I have attached a file with two examples.

[MSBuild Change Request.docx](https://github.com/Microsoft/msbuild/files/1110020/MSBuild.Change.Request.docx)

If have missed something or there is a better way, I'd love to hear it.

Start by reading the attached MSBuild Change Request.docx and compare the two examples it contains. Determine whether the requested macro for carrying current target(s) into a nested MSBuild invocation fits the existing target-execution model; done means the behavior is defined and supported by appropriate project-level examples or tests.

Written by the indexing model from the issue text.