Fix more -Wsign-compare warnings in heap, mips, base, etc.

src/mips64/simulator-mips64.cc

 // Copyright 2011 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 <limits.h>
 #include <stdarg.h>
 #include <stdlib.h>
 #include <cmath>
 
 #if V8_TARGET_ARCH_MIPS64
@@ skipping 4861 matching lines @@
       icount_++;
       InstructionDecode(instr);
       program_counter = get_pc();
     }
   } else {
     // FLAG_stop_sim_at is at the non-default value. Stop in the debugger when
     // we reach the particular instuction count.
     while (program_counter != end_sim_pc) {
       Instruction* instr = reinterpret_cast<Instruction*>(program_counter);
       icount_++;
-      if (icount_ == static_cast<uint64_t>(::v8::internal::FLAG_stop_sim_at)) {
+      if (icount_ == static_cast<int64_t>(::v8::internal::FLAG_stop_sim_at)) {
         MipsDebugger dbg(this);
         dbg.Debug();
       } else {
         InstructionDecode(instr);
       }
       program_counter = get_pc();
     }
   }
 }
 
@@ skipping 159 matching lines @@
 }
 
 
 #undef UNSUPPORTED
 }  // namespace internal
 }  // namespace v8
 
 #endif  // USE_SIMULATOR
 
 #endif  // V8_TARGET_ARCH_MIPS64