Fix a -Wsign-compare warning in adjustScopeMarkerForAdressSanitizer()

Source/platform/heap/ThreadState.cpp

Index: Source/platform/heap/ThreadState.cpp
diff --git a/Source/platform/heap/ThreadState.cpp b/Source/platform/heap/ThreadState.cpp
index a8a66cb67fced14b8a90e6cafc677c3325ace37f..f528c197442dd0958a59ad75648acd0a478dbd90 100644
--- a/Source/platform/heap/ThreadState.cpp
+++ b/Source/platform/heap/ThreadState.cpp
@@ -738,7 +738,7 @@ NO_SANITIZE_ADDRESS static void* adjustScopeMarkerForAdressSanitizer(void* scope
 
     // 256 is as good an approximation as any else.
     const size_t bytesToCopy = sizeof(Address) * 256;
-    if (start - end < bytesToCopy)
+    if (static_cast<size_t>(start - end) < bytesToCopy)
         return start;
 
     return end + bytesToCopy;