libbpf: Allow use of feature cache for non-token cases

Allow bpf object feat_cache assignment in BPF selftests
to simulate missing features via inclusion of libbpf_internal.h
and use of bpf_object_set_feat_cache() and bpf_object__sanitize_btf() to
test BTF sanitization for cases where missing features are simulated.

Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
Link: https://lore.kernel.org/r/20260408165735.843763-2-alan.maguire@oracle.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

src/libbpf_internal.h

@@ -414,6 +414,7 @@ struct kern_feature_cache {
 
 bool feat_supported(struct kern_feature_cache *cache, enum kern_feature_id feat_id);
 bool kernel_supports(const struct bpf_object *obj, enum kern_feature_id feat_id);
+void bpf_object_set_feat_cache(struct bpf_object *obj, struct kern_feature_cache *cache);
 
 int probe_kern_syscall_wrapper(int token_fd);
 int probe_memcg_account(int token_fd);
@@ -427,7 +428,7 @@ int libbpf__load_raw_btf(const char *raw_types, size_t types_len,
 int libbpf__load_raw_btf_hdr(const struct btf_header *hdr,
 			     const char *raw_types, const char *str_sec,
 			     const char *layout_sec, int token_fd);
-
+struct btf *bpf_object__sanitize_btf(struct bpf_object *obj, struct btf *orig_btf);
 int btf_load_into_kernel(struct btf *btf,
 			 char *log_buf, size_t log_sz, __u32 log_level,
 			 int token_fd);