[CMake][Standalone] Fixup r197395 for standalone build.

Standalone scripts shall be rewritten.
[CMake][Standalone] Fix llvm-tblgen's directory to use LLVM_TOOLS_BINARY_DIR instead of LLVM_BINARY_DIR.

LLVM_BINARY_DIR points OBJROOT.

FIXME: llvm-config should show *real* bindir with --bindir.
[CMake][Standalone] Import LLVM_LIT_TOOLS_DIR.