[CMake] Final dependency cleanup patch!

Summary:
This patch removes the over-specified dependencies from LLDBDependencies and instead relies on the dependencies as expressed in each library and tool.

This also removes the library looping in favor of allowing CMake to do its thing. I've tested this patch on Darwin, and found no issues, but since linker semantics vary by system I'll also work on testing it on other platforms too.

Help testing would be greatly appreciated.

Reviewers: labath, zturner

Subscribers: danalbert, srhines, mgorny, jgosnell, lldb-commits

Differential Revision: https://reviews.llvm.org/D29352

llvm-svn: 294515