[CMake] Aggregate options for LLDB in LLDBConfig.cmake

Summary: In preparation for LLDB.framework changes, collect options for LLDB in LLDBConfig.cmake (used for both, standalone and in-tree builds of LLDB).

Reviewers: JDevlieghere, aprantl, xiaobai

Reviewed By: aprantl

Subscribers: srhines, mgorny, lldb-commits, #lldb

Differential Revision: https://reviews.llvm.org/D55317

llvm-svn: 350389