[CMake] Introduce new scheme of LLVM_TOOLS_BINARY_DIR and LLVM_LIBRARY_DIR

  In LLVM build tree, they points corresponding INTDIR.

  In Clang standalone tree, they points external dir (llvm-config's --bindir and --libdir).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@199595 91177308-0d34-0410-b5e6-96231b3b80d8