Allow forcing the use of a simulator from the build script...

src/top.cc

Index: src/top.cc
===================================================================
--- src/top.cc	(revision 5700)
+++ src/top.cc	(working copy)
@@ -67,8 +67,12 @@
   c_entry_fp_ = 0;
   handler_ = 0;
 #ifdef USE_SIMULATOR
+#ifdef V8_TARGET_ARCH_ARM
   simulator_ = assembler::arm::Simulator::current();
-#endif  // USE_SIMULATOR
+#elif V8_TARGET_ARCH_MIPS
+  simulator_ = assembler::mips::Simulator::current();
+#endif
+#endif
 #ifdef ENABLE_LOGGING_AND_PROFILING
   js_entry_sp_ = 0;
 #endif
@@ -1066,8 +1070,12 @@
   // This might be just paranoia, but it seems to be needed in case a
   // thread_local_ is restored on a separate OS thread.
 #ifdef USE_SIMULATOR
+#ifdef V8_TARGET_ARCH_ARM
   thread_local_.simulator_ = assembler::arm::Simulator::current();
+#elif V8_TARGET_ARCH_MIPS
+  thread_local_.simulator_ = assembler::mips::Simulator::current();
 #endif
+#endif
   return from + sizeof(thread_local_);
 }