tools: bpftool: fix warning on struct bpf_prog_linfo definition

The following warning appears when compiling bpftool without BFD
support:

main.h:198:23: warning: 'struct bpf_prog_linfo' declared inside
    parameter list will not be visible outside of this definition or
    declaration
          const struct bpf_prog_linfo *prog_linfo,

Fix it by declaring struct bpf_prog_linfo even in the case BFD is not
supported.

Fixes: b053b43 ("bpf: libbpf: bpftool: Print bpf_line_info during prog dump")
Signed-off-by: Quentin Monnet <quentin.monnet@netronome.com>
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

tools/bpf/bpftool/main.h

@@ -147,8 +147,8 @@ int prog_parse_fd(int *argc, char ***argv);
 int map_parse_fd(int *argc, char ***argv);
 int map_parse_fd_and_info(int *argc, char ***argv, void *info, __u32 *info_len);
 
-#ifdef HAVE_LIBBFD_SUPPORT
 struct bpf_prog_linfo;
+#ifdef HAVE_LIBBFD_SUPPORT
 void disasm_print_insn(unsigned char *image, ssize_t len, int opcodes,
 		       const char *arch, const char *disassembler_options,
 		       const struct btf *btf,