bug: Hush suggest-attribute=format for __warn_printf()

Recent additions to this function cause GCC 14.3.0 to get excited
(W=1) and suggest a missing attribute:

	lib/bug.c: In function '__warn_printf':
	lib/bug.c:187:25: error: function '__warn_printf' be a candidate for 'gnu_printf' format attribute [-Werror=suggest-attribute=format]
	  187 |                         vprintk(fmt, *args);
	      |                         ^~~~~~~

Disable the diagnostic locally, following the pattern used for stuff
like va_format().

Fixes: 5c47b7f ("bug: Add BUG_FORMAT_ARGS infrastructure")
Signed-off-by: Brendan Jackman <jackmanb@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://patch.msgid.link/20251207-warn-printf-gcc-v1-1-b597d612b94b@google.com

Author: bjackman

lib/bug.c

@@ -173,6 +173,9 @@ struct bug_entry *find_bug(unsigned long bugaddr)
 	return module_find_bug(bugaddr);
 }
 
+__diag_push();
+__diag_ignore(GCC, all, "-Wsuggest-attribute=format",
+	      "Not a valid __printf() conversion candidate.");
 static void __warn_printf(const char *fmt, struct pt_regs *regs)
 {
 	if (!fmt)
@@ -192,6 +195,7 @@ static void __warn_printf(const char *fmt, struct pt_regs *regs)
 
 	printk("%s", fmt);
 }
+__diag_pop();
 
 static enum bug_trap_type __report_bug(struct bug_entry *bug, unsigned long bugaddr, struct pt_regs *regs)
 {