Enable CrossGen tests

parent #276 

Verified with "build.cmd verify" and crossgen generated all dlls successfully (although I got a bunch of warnings during generation).
Can we do crazy things with escaped quotes? Like something like:

```
string.Format("/C \\"{0}\\" crossgen --in \"{1}\"", )
```

What I'm trying to do there is put CMD-escaped quotes around the `{0}` param. Does that work?