1. Make sure that "dot" can be found in the path

1. Make sure that "dot" can be found in the path
2. Fix a bug where the lib directory specified also had to be cwd
3. Weight the output so archive->archive edges are shorter
4. Generate two different graphs: one for libraries, one for objects.
5. Adjust the properties of the graphs till it looks nice.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@19293 91177308-0d34-0410-b5e6-96231b3b80d8