Switch to the Debian default LLVM/Clang (#1017665)
doxygen does not seem to require a lot of changes for new versions of LLVM/Clang, and it is released quite often; hence, switch it to use the default version of LLVM/Clang in Debian rather than a precise version:
- no more needed to switch to new versions manually
- whenever the default version is bumped, doxygen can be rebuilt as part of the transition to the new default version
- slightly less bits to maintain in the Debian packaging
Edited by Pino Toscano