cmake: Create all output directories for Doxygen
CI builds intermittently fail with
error: Could not create output directory /.../doc/api/xml
or
error: Could not create output directory /.../doc/api/man
Fixes: #266 (closed) (I hope)
Signed-off-by: Simon McVittie smcv@collabora.com
/cc @rhabacker
Edited by Simon McVittie