[CMake] Prune LLVM_TOOLS_DIR and LLVM_LIBS_DIR in clang/test/CMakeLists.txt....

[CMake] Prune LLVM_TOOLS_DIR and LLVM_LIBS_DIR in clang/test/CMakeLists.txt. They are overridden in configure_lit_site_cfg().

llvm-svn: 199591