X87: add part of backend support for X87.

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 d37c9d77dcb59cda879f4bd696675b293881c9c2..8c7630b24f271a7f09934ceab9247aa8d4e70552 100644
--- a/src/x87/assembler-x87.h
+++ b/src/x87/assembler-x87.h
@@ -148,6 +148,13 @@ struct X87Register {
     return kMaxNumAllocatableRegisters;
   }
 
+
+  // TODO(turbofan): Proper support for float32.
+  static int NumAllocatableAliasedRegisters() {
+    return NumAllocatableRegisters();
+  }
+
+
   static int ToAllocationIndex(X87Register reg) {
     return reg.code_;
   }