More code for ia32, more shared code.

runtime/vm/assembler_x64.h

Index: runtime/vm/assembler_x64.h
===================================================================
--- runtime/vm/assembler_x64.h	(revision 8338)
+++ runtime/vm/assembler_x64.h	(working copy)
@@ -491,8 +491,14 @@
   }
 
   /*
-   * Macros for High-level operations.
+   * Macros for High-level operations and implemented on all architectures.
    */
+
+  void CompareRegisters(Register a, Register b);
+
+  // Issues a move instruction if 'to' is not the same as 'from'.
+  void MoveRegister(Register to, Register from);
+
   void AddImmediate(Register reg, const Immediate& imm);
 
   void Drop(intptr_t stack_elements);