Add support for XMM registers in SSA code generation pipeline.

runtime/vm/assembler_x64.h

Index: runtime/vm/assembler_x64.h
diff --git a/runtime/vm/assembler_x64.h b/runtime/vm/assembler_x64.h
index eef61110e30a84cdf1c1c77671849e40db7f8218..fce55d6867e49c54049d9b6ba537ba29ac8222b5 100644
--- a/runtime/vm/assembler_x64.h
+++ b/runtime/vm/assembler_x64.h
@@ -343,6 +343,8 @@ class Assembler : public ValueObject {
   void movsd(const Address& dst, XmmRegister src);
   void movsd(XmmRegister dst, XmmRegister src);
 
+  void movaps(XmmRegister dst, XmmRegister src);
+
   void addsd(XmmRegister dst, XmmRegister src);
   void subsd(XmmRegister dst, XmmRegister src);
   void mulsd(XmmRegister dst, XmmRegister src);
@@ -616,6 +618,8 @@ class Assembler : public ValueObject {
 
   static const char* RegisterName(Register reg);
 
+  static const char* XmmRegisterName(XmmRegister reg);
+
  private:
   AssemblerBuffer buffer_;
   int prolog_offset_;