stack(9): Disable KASAN in stack_capture()

When unwinding the stack, we may encounter a stack frame in a poisoned
region of the stack, triggering a false positive.

Reviewed by:	andrew, kib
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D30126

sys/x86/x86/stack_machdep.c

@@ -70,7 +70,7 @@ static struct mtx intr_lock;
 MTX_SYSINIT(intr_lock, &intr_lock, "stack intr", MTX_DEF);
 #endif
 
-static void
+static void __nosanitizeaddress
 stack_capture(struct thread *td, struct stack *st, register_t fp)
 {
 	x86_frame_t frame;