libbpf: Fix single-line struct definition output in btf_dump

btf_dump APIs emit unnecessary tabs when emitting struct/union
definition that fits on the single line. Before this patch we'd get:

struct blah {<tab>};

This patch fixes this and makes sure that we get more natural:

struct blah {};

Fixes: 44a726c3 ("bpftool: Print newline before '}' for struct with padding only fields")
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20221212211505.558851-2-andrii@kernel.org

tools/lib/bpf/btf_dump.c

@@ -959,9 +959,12 @@ static void btf_dump_emit_struct_def(struct btf_dump *d,
 	 * Keep `struct empty {}` on a single line,
 	 * only print newline when there are regular or padding fields.
 	 */
-	if (vlen || t->size)
+	if (vlen || t->size) {
 		btf_dump_printf(d, "\n");
 		btf_dump_printf(d, "%s}", pfx(lvl));
+	} else {
+		btf_dump_printf(d, "}");
+	}
 	if (packed)
 		btf_dump_printf(d, " __attribute__((packed))");
 }