[CMake] Distribution builds for LLDB standalone

Summary:
Enable `distribution` and `install-distribution` targets in LLDB standalone and pre-populate the cache accordingly on macOS.
Documentation for distribution builds is here: https://llvm.org/docs/BuildingADistribution.html

Reviewers: xiaobai, mgorny, JDevlieghere, davide, compnerd

Reviewed By: xiaobai, JDevlieghere

Subscribers: lldb-commits, #lldb

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D64399

llvm-svn: 365616