WIP: Add CMake doxygen error check #988

[nilason]

This PR adds doxygen error check for CMake builds with a new target (make doxygen-checked), similar to what’s implemented for autotools.

Implemented with only CMake code it’s supposed to work on any platform, but should be tested.

This is a mirror of https://git.osgeo.org/gitea/geos/geos/pulls/95. Opened the PR here too for testing purposes.

[dbaston]

What do you think about registering this as a test, like this?

    add_custom_target(docs
        COMMAND ${DOXYGEN_EXECUTABLE} ${CMAKE_CURRENT_BINARY_DIR}/Doxyfile
        DEPENDS geos
        BYPRODUCTS ${DOXYGEN_LOGFILE})

    add_test(NAME test_docs
             COMMAND ${CMAKE_COMMAND}
                 -D DOXYGEN_LOGFILE=${DOXYGEN_LOGFILE}
                 -P "${CMAKE_CURRENT_BINARY_DIR}/${CHECK_ERROR_SCRIPT}")

[nilason]

Makes sense, a test is after all what it is. Updated as recommended.
Thanks!