The paths of the doxygen tag files for sphinxcontrib-doxygen must be
absolute or relative the the current working directory. However, when
libcamera is built as a subproject, the current working directory
is the top-level build directory. Thus the paths for the tag files
will not be correct.
Fix that by using `configure_file()` to generate the final sphinx
configuration with the appropriate paths queried from meson.
Fixes: 0382d215db ("Documentation: Use Sphinx doxylink to generate links to doxygen")
Signed-off-by: Barnabás Pőcze <barnabas.pocze@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>