bugs/x86: Augment warnings output by concatenating 'cond_str' with the regular __FILE__ string in _BUG_FLAGS()

This allows the reuse of the UD2 based 'struct bug_entry' low-overhead
_BUG_FLAGS() implementation and string-printing backend, without
having to add a new field.

An example:

If we have the following WARN_ON_ONCE() in kernel/sched/core.c:

	WARN_ON_ONCE(idx < 0 && ptr);

Then previously _BUG_FLAGS() would store this string in bug_entry::file:

	"kernel/sched/core.c"

After this patch, it would store and print:

	"[idx < 0 && ptr] kernel/sched/core.c"

Which is an extended string that will be printed in warnings.

Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Cc: linux-arch@vger.kernel.org
Link: https://lore.kernel.org/r/20250515124644.2958810-6-mingo@kernel.org

arch/x86/include/asm/bug.h

@@ -50,7 +50,7 @@ do {									\
 		     "\t.org 2b+%c3\n"					\
 		     ".popsection\n"					\
 		     extra						\
-		     : : "i" (__FILE__), "i" (__LINE__),		\
+		     : : "i" (WARN_CONDITION_STR(cond_str) __FILE__), "i" (__LINE__),		\
 			 "i" (flags),					\
 			 "i" (sizeof(struct bug_entry)));		\
 } while (0)