Fix x64 breakage.

src/mark-compact.cc

Index: src/mark-compact.cc
diff --git a/src/mark-compact.cc b/src/mark-compact.cc
index 8bd8b95a1f7e1576c4820d2d5adfad08df2e863e..e625ddfca10f8c767bfd89b986ae5619394411fb 100644
--- a/src/mark-compact.cc
+++ b/src/mark-compact.cc
@@ -3078,7 +3078,7 @@ void MarkCompactCollector::EvacuatePages() {
     // crash in concurrent sweeping.
     CHECK(p->IsEvacuationCandidate() ||
           p->IsFlagSet(Page::RESCAN_ON_EVACUATION));
-    CHECK_EQ(p->parallel_sweeping(), 0);
+    CHECK_EQ(static_cast<int>(p->parallel_sweeping()), 0);
     if (p->IsEvacuationCandidate()) {
       // During compaction we might have to request a new page.
       // Check that space still have room for that.