[CMake] Cleanup check-lldb targets

Summary:
This patch adds the following fixes to the check-lldb targets:

* Adds missing dependencies on lldb tools so they get built before tests execute
* Adds Ninja USES_TERMINAL to the target so that the output streams to stdout as it executes
* Uses a generator expression to find the lldb executable, this is more robust than constructing the path manually

Reviewers: tfiala, zturner

Subscribers: mgorny, lldb-commits

Differential Revision: https://reviews.llvm.org/D25490

llvm-svn: 284046