VM: Fix simdbc and darkp builds.

runtime/vm/kernel_isolate.cc

Index: runtime/vm/kernel_isolate.cc
diff --git a/runtime/vm/kernel_isolate.cc b/runtime/vm/kernel_isolate.cc
index 03b6565aeae5c0c2f09c87edc797074e212c3620..d0a09f80faa1d4cff8dcc778103244c473c21211 100644
--- a/runtime/vm/kernel_isolate.cc
+++ b/runtime/vm/kernel_isolate.cc
@@ -76,7 +76,11 @@ class RunKernelTask : public ThreadPool::Task {
     api_flags.enable_asserts = false;
     api_flags.enable_error_on_bad_type = false;
     api_flags.enable_error_on_bad_override = false;
+#if defined(DART_PRECOMPILER)
+    api_flags.use_field_guards = false;
+#else
     api_flags.use_field_guards = true;
+#endif
 
     isolate = reinterpret_cast<Isolate*>(create_callback(
         KernelIsolate::kName, NULL, NULL, NULL, &api_flags, NULL, &error));