Build qdoc in qt5-tools. This is needed to make Qt5 examples appear in Qt Creator.
It's different. By including llvm-clang-devel we use GCC to build the package while allowing qdoc to use clang's parsing functions for its jobs. If we set clang: yes, we're both allowing qdoc to use clang (because we're still including llvm-clang-devel) AND we're building the whole package with clang.
So if you're OK with building qt5-tools with clang, all great, otherwise including llvm-clang-devel is the right choice.