Add a kSimd128 machine type for Turbofan.

src/x87/assembler-x87.h

Index: src/x87/assembler-x87.h
diff --git a/src/x87/assembler-x87.h b/src/x87/assembler-x87.h
index 0301dda46ecc2f0e793e452ef12ccd09e38d6508..4921e82d197b019785a17a3bd7a7339463e74bc6 100644
--- a/src/x87/assembler-x87.h
+++ b/src/x87/assembler-x87.h
@@ -186,6 +186,9 @@ const DoubleRegister no_double_reg = {DoubleRegister::kCode_no_reg};
 
 typedef DoubleRegister X87Register;
 
+// TODO(x87) Define SIMD registers.
+typedef DoubleRegister Simd128Register;
+
 enum Condition {
   // any value < 0 is considered no_condition
   no_condition  = -1,