Fix debugger stub patching on x64 architecture

runtime/vm/code_patcher_arm.cc

Index: runtime/vm/code_patcher_arm.cc
===================================================================
--- runtime/vm/code_patcher_arm.cc	(revision 31811)
+++ runtime/vm/code_patcher_arm.cc	(working copy)
@@ -46,6 +46,17 @@
 }
 
 
+int32_t CodePatcher::GetPoolOffsetAt(uword return_address) {
+  UNIMPLEMENTED();
+  return 0;
+}
+
+
+void CodePatcher::SetPoolOffsetAt(uword return_address, int32_t offset) {
+  UNIMPLEMENTED();
+}
+
+
 void CodePatcher::InsertCallAt(uword start, uword target) {
   // The inserted call should not overlap the lazy deopt jump code.
   ASSERT(start + CallPattern::kFixedLengthInBytes <= target);