[CMake] Prune deprecate usage of CMAKE_RUNTIME_OUTPUT_DIRECTORY.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@199592 91177308-0d34-0410-b5e6-96231b3b80d8
[CMake] Deprecate LLVM_TOOLS_BINARY_DIR.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@199593 91177308-0d34-0410-b5e6-96231b3b80d8
[CMake] Add comments in llvm/CMakeLists.txt.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@199594 91177308-0d34-0410-b5e6-96231b3b80d8