Fix building with GCC 3.x

src/mark-compact.cc

Index: src/mark-compact.cc
diff --git a/src/mark-compact.cc b/src/mark-compact.cc
index 6c16f61d25f0f1c80f5a62af7121230698b5835c..ba7fcf0b32fde861d6bf94fc0e7d176aa98f19a2 100644
--- a/src/mark-compact.cc
+++ b/src/mark-compact.cc
@@ -577,7 +577,7 @@ void MarkCompactCollector::CollectEvacuationCandidates(PagedSpace* space) {
     p->ClearEvacuationCandidate();
 
     if (FLAG_stress_compaction) {
-      int counter = space->heap()->ms_count();
+      unsigned int counter = space->heap()->ms_count();
       uintptr_t page_number = reinterpret_cast<uintptr_t>(p) >> kPageSizeBits;
       if ((counter & 1) == (page_number & 1)) fragmentation = 1;
     } else if (mode == REDUCE_MEMORY_FOOTPRINT) {