Summary:
This creates a separate LLDB_TEST_SRC var to match the existing LLDB_TEST var. LLDB_TEST points to the test framework, LLDB_TEST_SRC points to the tests themselves.
The var points to the same place, but a future patch will move the tree + update var.
Reviewers: labath, JDevlieghere
Reviewed By: labath
Subscribers: merge_guards_bot, lldb-commits
Tags: #lldb
Differential Revision: https://reviews.llvm.org/D71150