Support encoding of BTF layout data via btf__new_empty_opts(). Current supported opts are base_btf and add_layout. Layout information is maintained in btf.c in the layouts[] array; when BTF is created with the add_layout option it represents the current view of supported BTF kinds. Signed-off-by: Alan Maguire <alan.maguire@oracle.com> Signed-off-by: Andrii Nakryiko <andrii@kernel.org> Link: https://lore.kernel.org/bpf/20260326145444.2076244-5-alan.maguire@oracle.com