Fix -Wsign-compare bugs with GCC 4.9.2

src/compiler/register-allocator.cc

Index: src/compiler/register-allocator.cc
diff --git a/src/compiler/register-allocator.cc b/src/compiler/register-allocator.cc
index dd526cd47b88bcdcd274ef235d26867e3e88668a..28007d47fa11aadc60c0781e3793d76a13d39880 100644
--- a/src/compiler/register-allocator.cc
+++ b/src/compiler/register-allocator.cc
@@ -2218,7 +2218,7 @@ float GreedyAllocator::CalculateSpillWeight(LiveRange* range) {
 
   // GetLiveRangeSize is DCHECK-ed to not be 0
   unsigned range_size = GetLiveRangeSize(range);
-  DCHECK_NE(0, range_size);
+  DCHECK_NE(0U, range_size);
 
   return static_cast<float>(use_count) / static_cast<float>(range_size);
 }