* gnu/packages/doxygen.scm (doxygen): Add propagated input graphviz.
* gnu/packages/doxygen.scm: New file. * gnu/packages/patches/doxygen-test.patch, gnu/packages/patches/doxygen-tmake.patch: New files. * gnu-system.am (GNU_SYSTEM_MODULES, dist_patch_DATA): Register the new files.