This prepares for backporting parts of PR10155, which change the Doxyfile from static to being generated by the build system. When the Doxyfile is static, it can be pulled from the repo without any changes and compiled by doxygen (which the host does today). D3508 changes Doxyfile -> Doxyfile.in which must be compiled by the build system prior to passing to doxygen. In a more perfect world, we would have the build prepared by another machine and the Doxyfile passed to the host, but that infra is not available today. This change is good enough to get us there since hosting these pages is low-impact anyway.