MSBuild uses wrong order when Cleaning, causing unregistration of COM components to fail.

When having the "Register for COM interop" checked in C# projects, where there are multiple projects that may have dependencies on each other, the order in which the projects are cleaned when running MSBuild on the solution is incorrect.

Attached is a simple solution containing three projects, ComRegTest, ComRegTest2, and ComRegTest3.
The ComRegTest2 project references both of the others. When building the projects the build order is correct:
1. ComRegTest
2. ComRegTest3
3. ComRegTest2

But when running `msbuild ComRegTest.sln /t:Clean /m:1` the order in which the projects are cleaned are:
1. ComRegTest3
2. ComRegTest2
3. ComRegTest1

This causes an error to occur when cleaning ComRegTest2, saying:

```
error MSB3395: Cannot unregister asse mbly "D:\Projects\ComRegTest\bin\ComRegTest2.dll". Could not load file or assembly 'ComRegTest3, Version=1.0.0.0, Culture=neut ral, PublicKeyToken=null' or one of its dependencies. The system cannot find the file specified.
```

This problem does not occur when cleaning from within Visual Studio 2015.

[ComRegTest.zip](https://github.com/Microsoft/msbuild/files/544987/ComRegTest.zip)