Add ObjectPool tag for external labels. Use LoadExternalLabel for native calls...

runtime/vm/intermediate_language_arm64.cc

Index: runtime/vm/intermediate_language_arm64.cc
diff --git a/runtime/vm/intermediate_language_arm64.cc b/runtime/vm/intermediate_language_arm64.cc
index 9587767ac1070d8973a83f837954bd40efd9113a..10bd177a37b59158c01821b7f86ae6a299d61a32 100644
--- a/runtime/vm/intermediate_language_arm64.cc
+++ b/runtime/vm/intermediate_language_arm64.cc
@@ -814,7 +814,8 @@ void NativeCallInstr::EmitNativeCode(FlowGraphCompiler* compiler) {
     }
 #endif
   }
-  __ LoadImmediate(R5, entry);
+  ExternalLabel label(entry);
+  __ LoadExternalLabel(R5, &label);
   __ LoadImmediate(R1, argc_tag);
   compiler->GenerateCall(token_pos(),
                          *stub_entry,
@@ -839,8 +840,9 @@ void StringFromCharCodeInstr::EmitNativeCode(FlowGraphCompiler* compiler) {
   ASSERT(compiler->is_optimizing());
   const Register char_code = locs()->in(0).reg();
   const Register result = locs()->out(0).reg();
-  __ LoadImmediate(
-      result, reinterpret_cast<uword>(Symbols::PredefinedAddress()));
+
+  ExternalLabel label(reinterpret_cast<uword>(Symbols::PredefinedAddress()));
+  __ LoadExternalLabel(result, &label);
   __ AddImmediate(
       result, result, Symbols::kNullCharCodeSymbolOffset * kWordSize);
   __ SmiUntag(TMP, char_code);  // Untag to use scaled adress mode.