[turbofan] Add backend support for float32.

src/x64/assembler-x64.h

Index: src/x64/assembler-x64.h
diff --git a/src/x64/assembler-x64.h b/src/x64/assembler-x64.h
index b2a97cc64208572b297a65ea73a07f52dc61f0f9..568719eae473a59d82d23b94a421c63ce8c94da3 100644
--- a/src/x64/assembler-x64.h
+++ b/src/x64/assembler-x64.h
@@ -200,6 +200,11 @@ struct XMMRegister {
     return kMaxNumAllocatableRegisters;
   }
 
+  // TODO(turbofan): Proper support for float32.
+  static int NumAllocatableAliasedRegisters() {
+    return NumAllocatableRegisters();
+  }
+
   static int ToAllocationIndex(XMMRegister reg) {
     DCHECK(reg.code() != 0);
     return reg.code() - 1;