malloc_debug: Implement alloc/free stack traces in guarded heap.

When configured to do so (using heap_debug_set_stack_trace_depth(depth)
or MALLOC_DEBUG=s<depth>) the guarded heap now captures stack traces on
alloc and free.

A crash due to hitting a guard page or an already freed page now dumps
these stack traces. In the case of use-after-free one can therefore see
both where the allocation was done and where it was freed.

Note that there is a hardcoded maximum stack trace depth of 50 and that
the alloc stack trace takes away space from the free stack trace which
uses up the rest of that maximum.

headers/posix/malloc_debug.h

@@ -30,6 +30,8 @@ void *heap_debug_malloc_with_guard_page(size_t size);
 status_t heap_debug_get_allocation_info(void *address, size_t *size,
 	thread_id *thread);
 
+status_t heap_debug_set_stack_trace_depth(size_t stackTraceDepth);
+
 #ifdef __cplusplus
 }
 #endif