[CMake][Standalone] Introduce check-all.
[CMake] Always set CMAKE_INCLUDE_CURRENT_DIR.
Revert r113780, "Recognize .ll as input files. Handle %test_debuginfo on a RUN command line."

This feature has been unused anymore.
check-clang doesn't require neither llvm_src_root nor llvm_obj_root.
clang-check: Unittests doesn't requires tools.