x86/unwinder/guess: Prevent using CONFIG_UNWINDER_GUESS=y with CONFIG_STACKDEPOT=y

Stackdepot doesn't work well with CONFIG_UNWINDER_GUESS=y.
The 'guess' unwinder generate awfully large and inaccurate stacktraces,
thus stackdepot can't deduplicate stacktraces because they all look like
unique. Eventually stackdepot reaches its capacity limit:

  WARNING: CPU: 0 PID: 545 at lib/stackdepot.c:119 depot_save_stack+0x28e/0x550
  Call Trace:
   ? kasan_kmalloc+0x144/0x160
   ? depot_save_stack+0x1f5/0x550
   ? do_raw_spin_unlock+0xda/0xf0
   ? preempt_count_sub+0x13/0xc0

  <...90 lines...>

   ? do_raw_spin_unlock+0xda/0xf0

Add a STACKDEPOT=n dependency to UNWINDER_GUESS to avoid the problem.

Reported-by: kernel test robot <xiaolong.ye@intel.com>
Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Acked-by: Dmitry Vyukov <dvyukov@google.com>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20171130123554.4330-1-aryabinin@virtuozzo.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/Kconfig.debug

@@ -400,6 +400,7 @@ config UNWINDER_FRAME_POINTER
 config UNWINDER_GUESS
 	bool "Guess unwinder"
 	depends on EXPERT
+	depends on !STACKDEPOT
 	---help---
 	  This option enables the "guess" unwinder for unwinding kernel stack
 	  traces.  It scans the stack and reports every kernel text address it