Generate some intrinsics using our IR.

runtime/vm/assembler_arm64.h

Index: runtime/vm/assembler_arm64.h
===================================================================
--- runtime/vm/assembler_arm64.h	(revision 39909)
+++ runtime/vm/assembler_arm64.h	(working copy)
@@ -1147,6 +1147,13 @@
     kNotPatchable,
   };
 
+  bool allow_constant_pool() const {
+    return allow_constant_pool_;
+  }
+  void set_allow_constant_pool(bool b) {
+    allow_constant_pool_ = b;
+  }
+
   void LoadWordFromPoolOffset(Register dst, Register pp, uint32_t offset);
   void LoadWordFromPoolOffsetFixed(Register dst, Register pp, uint32_t offset);
   intptr_t FindExternalLabel(const ExternalLabel* label,
@@ -1315,6 +1322,8 @@
 
   GrowableArray<CodeComment*> comments_;
 
+  bool allow_constant_pool_;
+
   void AddSubHelper(OperandSize os, bool set_flags, bool subtract,
                     Register rd, Register rn, Operand o) {
     ASSERT((rd != R31) && (rn != R31));