tools/resolve_btfids: Install subcmd headers

tools/resolve_btfids: Install subcmd headers

commit af03299d8536d62b49c7f3cb929349eb2d66bcd5 upstream.

Previously tools/lib/subcmd was added to the include path, switch to
installing the headers and then including from that directory. This
avoids dependencies on headers internal to tools/lib/subcmd. Add the
missing subcmd directory to the affected #include.

Signed-off-by: Ian Rogers <irogers@google.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Link: https://lore.kernel.org/bpf/20230124064324.672022-1-irogers@google.com
Cc: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>