[turbofan] Create ExplicitOperands to specify operands without virtual registers

src/compiler/register-allocator-verifier.h

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_REGISTER_ALLOCATOR_VERIFIER_H_
 #define V8_REGISTER_ALLOCATOR_VERIFIER_H_
 
 #include "src/zone-containers.h"
 
 namespace v8 {
@@ skipping 17 matching lines @@
     kImmediate,
     kRegister,
     kFixedRegister,
     kDoubleRegister,
     kFixedDoubleRegister,
     kSlot,
     kDoubleSlot,
     kFixedSlot,
     kNone,
     kNoneDouble,
+    kExplicit,
     kSameAsFirst
   };
 
   struct OperandConstraint {
     ConstraintType type_;
     int value_;  // subkind index when relevant
     int virtual_register_;
   };
 
   struct InstructionConstraint {
@@ skipping 28 matching lines @@
   Constraints constraints_;
 
   DISALLOW_COPY_AND_ASSIGN(RegisterAllocatorVerifier);
 };
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif