heap: Fix by-word error in IsOnStack() for unsafe stack

Bug: chromium:1300105
Change-Id: I89d08662a81bec6da7f1565c8fc582edc69781d5
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3485682
Auto-Submit: Anton Bikineev <bikineev@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79244}

src/heap/base/stack.cc

@@ -40,7 +40,7 @@ bool Stack::IsOnStack(void* slot) const {
 #if defined(__has_feature)
 #if __has_feature(safe_stack)
   if (__builtin___get_unsafe_stack_top() >= slot &&
-      slot > __builtin___get_unsafe_stack_ptr()) {
+      slot >= __builtin___get_unsafe_stack_ptr()) {
     return true;
   }
 #endif  // __has_feature(safe_stack)