FindDoxygen: Create DOXYGEN_OUTPUT_DIRECTORY if it doesn't exist
If the doxygen output directory does not exist, create it prior to running the doxygen commands.
Topic-rename: FindDoxygen-create-output-dir
Edited by Brad King
If the doxygen output directory does not exist, create it prior to running the doxygen commands.
Topic-rename: FindDoxygen-create-output-dir