[x64] simply tweak materialization of float/double constants

src/x64/assembler-x64-inl.h

Index: src/x64/assembler-x64-inl.h
diff --git a/src/x64/assembler-x64-inl.h b/src/x64/assembler-x64-inl.h
index b64bbfb664f55797d179ac6e2beab1ce1c33fc74..c3d2cdf2eba0cf8b8a51428497d916f99bb3d4bf 100644
--- a/src/x64/assembler-x64-inl.h
+++ b/src/x64/assembler-x64-inl.h
@@ -179,6 +179,11 @@ void Assembler::emit_optional_rex_32(Register rm_reg) {
 }
 
 
+void Assembler::emit_optional_rex_32(XMMRegister rm_reg) {
+  if (rm_reg.high_bit()) emit(0x41);
+}
+
+
 void Assembler::emit_optional_rex_32(const Operand& op) {
   if (op.rex_ != 0) emit(0x40 | op.rex_);
 }