[LOG4CXX-548] Reproducible Doxygen doc generation

[coldtobi]

The way the doxygen documenation is generated with CMake, it is unfortunatly
not reproducible (as in https://reproducible-builds.org/).

This is a regression as log4cxx has been previously reproducible (at least on
Debian –
https://tests.reproducible-builds.org/debian/rb-pkg/experimental/amd64/log4cxx.html)

The problem is that doxygen's configure has several absolute paths, which it
then bakes into the generated documentation, for example in this snippt, the
bold part dependent on the build path:

[rm5248]

The patch as given requires CMake 3.20+, but doesn't update the minimum required version. I'd like to not have to bump the CMake version if possible.

I changed the cmake_path directive to file(RELATIVE_PATH LOG4CXX_REL_BIN_TO_SRC_DIR "${LOG4CXX_SOURCE_DIR}" "${CMAKE_CURRENT_BINARY_DIR}") on my side which seems to work fine, would you be able to validate that? I don't see where the particular example that you showed is coming in from, that only seems to be a problem with the MapFilter page.

[coldtobi]

The patch as given requires CMake 3.20+, but doesn't update the minimum required version. I'd like to not have to bump the CMake version if possible.

Ack.

I changed the cmake_path directive to file(RELATIVE_PATH LOG4CXX_REL_BIN_TO_SRC_DIR "${LOG4CXX_SOURCE_DIR}" "${CMAKE_CURRENT_BINARY_DIR}") on my side which seems to work fine, would you be able to validate that?

LGTM, it builds reproducible as well on my machine. I'll update my PR accordingly.

I don't see where the particular example that you showed is coming in from, that only seems to be a problem with the MapFilter page.

It seems everything in site/markdown triggering the differences... Here's a (local created) complete diff: https://pastebin.com/6BLaEa0K. (So it is quite possible that only the INPUT configuration of Doxyfile.in would need to be relative, but I believe making the other relative won't hurt.)