pahole: Distilled_base btf_feature should be reported for libbpf > 1.5

Alexei ran into issues [1] generating distilled base BTF with pahole built
against an older < 1.5 libbpf.  For older libbpf, we cannot support
distilled base BTF (since the library API btf__distill_base() is not
present) so we should not report it as a feature in that case.

[1] https://lore.kernel.org/bpf/CAADnVQKFjK8BnZ-rYzXKv-Zdw=HBJRoJ7jo5PN+0P6+qpJOxNg@mail.gmail.com/

Reported-by: Alexei Starovoitov <[email protected]>
Signed-off-by: Alan Maguire <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>

Author: alan-maguire

pahole.c

@@ -1206,7 +1206,9 @@ struct btf_feature {
 	BTF_DEFAULT_FEATURE(consistent_func, skip_encoding_btf_inconsistent_proto, false),
 	BTF_DEFAULT_FEATURE(decl_tag_kfuncs, btf_decl_tag_kfuncs, false),
 	BTF_NON_DEFAULT_FEATURE(reproducible_build, reproducible_build, false),
+#if LIBBPF_MAJOR_VERSION >= 1 && LIBBPF_MINOR_VERSION >= 5
 	BTF_NON_DEFAULT_FEATURE(distilled_base, btf_gen_distilled_base, false),
+#endif
 	BTF_NON_DEFAULT_FEATURE(global_var, encode_btf_global_vars, false),
 };