Disable all dependency output options when using the Tooling library.

It isn't appropriate for a tool to be stomping over the dependency files,
especially if the actual build uses a compiler other than Clang or the tool
cannot find all the headers for some reason (which would cause the existing
dependency file to be deleted).

If a tool actually needs to care about dependency files we can think about
adding a mechanism for getting to this information.

Differential Revision: http://llvm-reviews.chandlerc.com/D2912