libbpf: Expose btf_type_by_id() internally

btf_type_by_id() is internal-only convenience API returning non-const pointer
to struct btf_type. Expose it outside of btf.c for re-use.

Signed-off-by: Andrii Nakryiko <[e-mail]>
Signed-off-by: Alexei Starovoitov <[e-mail]>
Link: https://lore.kernel.org/bpf/[e-mail]

tools/lib/bpf/btf.c

···
 }
 
 /* internal helper returning non-const pointer to a type */
-static struct btf_type *btf_type_by_id(struct btf *btf, __u32 type_id)
+struct btf_type *btf_type_by_id(struct btf *btf, __u32 type_id)
 {
 	if (type_id == 0)
 		return &btf_void;

tools/lib/bpf/libbpf_internal.h

···
 	return realloc(ptr, total);
 }
 
+struct btf;
+struct btf_type;
+
+struct btf_type *btf_type_by_id(struct btf *btf, __u32 type_id);
+
 void *btf_add_mem(void **data, size_t *cap_cnt, size_t elem_sz,
 		  size_t cur_cnt, size_t max_cnt, size_t add_cnt);
 int btf_ensure_mem(void **data, size_t *cap_cnt, size_t elem_sz, size_t need_cnt);