haiku/build/config_headers/ReadMe

To customize the settings defined in these headers, create a folder
"user_config_headers" in the "build" folder and copy the headers you want to
modify into that folder. Your custom headers will be ignored by the version
control system and the build system will automatically use them instead of the
original ones. But be aware that when changes are commited to the files in
"config_headers", you will have to apply them to your custom headers manually.