qttools: enable clang/qdoc if meta-clang is in layers
qttools: enable clang/qdoc if meta-clang is in layers

We need qt-help native support  for kdevelop and others

Signed-off-by: Andreas Müller <d72a15aaaca3a7afa855175c72dc8d2e05931e32@gmail.com>

schnitzeltony/meta-qt5-extra,schnitzeltony/meta-qt5-extra,schnitzeltony/meta-qt5-extra