tools: bpftool: fix -Wmissing declaration warnings

Help compiler check arguments for several utility functions used to
print items to the console by adding the "printf" attribute when
declaring those functions.

Also, declare as "static" two functions that are only used in prog.c.

All of them discovered by compiling bpftool with
-Wmissing-format-attribute -Wmissing-declarations.

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/xlated_dumper.c

@@ -81,7 +81,7 @@ struct kernel_sym *kernel_syms_search(struct dump_data *dd,
 		       sizeof(*dd->sym_mapping), kernel_syms_cmp) : NULL;
 }
 
-static void print_insn(void *private_data, const char *fmt, ...)
+static void __printf(2, 3) print_insn(void *private_data, const char *fmt, ...)
 {
 	va_list args;
 
@@ -90,7 +90,7 @@ static void print_insn(void *private_data, const char *fmt, ...)
 	va_end(args);
 }
 
-static void
+static void __printf(2, 3)
 print_insn_for_graph(void *private_data, const char *fmt, ...)
 {
 	char buf[64], *p;
@@ -121,7 +121,8 @@ print_insn_for_graph(void *private_data, const char *fmt, ...)
 	printf("%s", buf);
 }
 
-static void print_insn_json(void *private_data, const char *fmt, ...)
+static void __printf(2, 3)
+print_insn_json(void *private_data, const char *fmt, ...)
 {
 	unsigned int l = strlen(fmt);
 	char chomped_fmt[l];