[turbofan] Fix more -Wsign-compare warnings.

test/unittests/compiler/mips64/instruction-selector-mips64-unittest.cc

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file
 
 #include "test/unittests/compiler/instruction-selector-unittest.h"
 
 namespace v8 {
 namespace internal {
 namespace compiler {
 
@@ skipping 314 matching lines @@
 
 TEST_P(InstructionSelectorCmpTest, Parameter) {
   const IntCmp cmp = GetParam();
   const MachineType type = cmp.mi.machine_type;
   StreamBuilder m(this, type, type, type);
   m.Return((m.*cmp.mi.constructor)(m.Parameter(0), m.Parameter(1)));
   Stream s = m.Build();
 
   if (FLAG_debug_code &&
       type.representation() == MachineRepresentation::kWord32) {
-    ASSERT_EQ(6, s.size());
+    ASSERT_EQ(6U, s.size());
 
     EXPECT_EQ(cmp.mi.arch_opcode, s[0]->arch_opcode());
     EXPECT_EQ(2U, s[0]->InputCount());
     EXPECT_EQ(1U, s[0]->OutputCount());
 
     EXPECT_EQ(kMips64Dshl, s[1]->arch_opcode());
     EXPECT_EQ(2U, s[1]->InputCount());
     EXPECT_EQ(1U, s[1]->OutputCount());
 
     EXPECT_EQ(kMips64Dshl, s[2]->arch_opcode());
@@ skipping 1561 matching lines @@
 #endif
 
       ASSERT_EQ(1U, s[0]->OutputCount());
     }
   }
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8