It complains even when Doxygen is installed and we don't need it for anything
anyway, so just remove it.

--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -135,11 +135,11 @@
   message(STATUS "pdflatex needed. The generation process will be skipped.")
 endif()
 
-find_package(Doxygen
-             REQUIRED dot)
-if (DOXYGEN_FOUND)
-  message(status "Doxygen found: ${DOXYGEN_EXECUTABLE}")
-endif()
+#find_package(Doxygen  XXX-Patched
+#             REQUIRED dot)
+#if (DOXYGEN_FOUND)
+#  message(status "Doxygen found: ${DOXYGEN_EXECUTABLE}")
+#endif()
 
 if (${CMAKE_SYSTEM_NAME} STREQUAL "Linux")
   find_package(Libatomic)