Fix more -Werror=sign-compare bugs with GCC 4.9.2

src/heap/identity-map.cc

Index: src/heap/identity-map.cc
diff --git a/src/heap/identity-map.cc b/src/heap/identity-map.cc
index e968989f97f5ae5b9ab930bc772ae6ca793f75a9..9840d74a3c13a974ef8a2cc1abb5c94becfc8d93 100644
--- a/src/heap/identity-map.cc
+++ b/src/heap/identity-map.cc
@@ -38,7 +38,7 @@ IdentityMapBase::RawEntry IdentityMapBase::Insert(Handle<Object> key) {
 
 int IdentityMapBase::Hash(Object* address) {
   uintptr_t raw_address = reinterpret_cast<uintptr_t>(address);
-  CHECK_NE(0, raw_address);  // Cannot store Smi 0 as a key here, sorry.
+  CHECK_NE(0U, raw_address);  // Cannot store Smi 0 as a key here, sorry.
   // Xor some of the upper bits, since the lower 2 or 3 are usually aligned.
   return static_cast<int>((raw_address >> 11) ^ raw_address);
 }