x86/bug: Add printf() validation to HAVE_ARCH_BUG_FORMAT_ARGS WARNs

x86/bug: Add printf() validation to HAVE_ARCH_BUG_FORMAT_ARGS WARNs

Add explicit printf() validation for x86-64's newfangled WARN
implementation, as most (all?) compilers fail to detect basic formatting
issues without the annotation.  E.g. even goofs like printing a u64 as a
string aren't detected:

  WARN_ONCE(1, "Bad message, %s", vcpu->arch.last_guest_tsc);

32-bit x86 doesn't support HAVE_ARCH_BUG_FORMAT_ARGS and uses generic
implementations that provide printf() validation. This means there's
now a big blind spot is code that is strictly x86-64. Inconveniently,
new features are also frequently x86-64-only.

Fix the blind 64-bit blind spot.

[ dhansen: changelog tweaks to flesh out the 64-bit-only details ]

Fixes: 5b472b6e5bd9 ("x86_64/bug: Implement __WARN_printf()")
Fixes: 11bb4944f014 ("x86/bug: Implement WARN_ONCE()")
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
Link: https://lore.kernel.org/all/adc1IrD8uqWdaOKv@yzhao56-desk.sh.intel.com
Link: https://patch.msgid.link/20260423145419.459988-2-seanjc@google.com