Use flat Doxygen builds
Building 4K subdirectories per category is very slow.
@@ -61,7 +61,7 @@ OUTPUT_DIRECTORY = @DOX_OUTPUT_DIRECTORY@
# source files, where putting all generated files in the same directory would
# otherwise cause performance problems for the file system.
-CREATE_SUBDIRS = YES
+CREATE_SUBDIRS = NO
# The OUTPUT_LANGUAGE tag is used to specify the language in which all
# documentation generated by doxygen is written. Doxygen will use this
