Fix FTBFS with CMake 4
Closes: #1112811
It requires additional missing Build-Depends: to doxygen Without it, CMake 4 raises an error:
CMake Error at doc/CMakeLists.txt:18 (ADD_DEPENDENCIES): The dependency target "doc-c" of target "doc" does not exist.
Signed-off-by: Kentaro Hayashi kenhys@xdump.org