[turbofan] Use special constant type for RPO block number operands.

src/compiler/arm/code-generator-arm.cc

Index: src/compiler/arm/code-generator-arm.cc
diff --git a/src/compiler/arm/code-generator-arm.cc b/src/compiler/arm/code-generator-arm.cc
index 8934b187d564f308dc55cdd02bd566b4c9f03cd3..28584259a9fda7d1a1da1beef81042329a5420c7 100644
--- a/src/compiler/arm/code-generator-arm.cc
+++ b/src/compiler/arm/code-generator-arm.cc
@@ -77,6 +77,7 @@ class ArmOperandConverter FINAL : public InstructionOperandConverter {
       case Constant::kInt64:
       case Constant::kExternalReference:
       case Constant::kHeapObject:
+      case Constant::kRpoNumber:
         break;
     }
     UNREACHABLE();
@@ -821,6 +822,9 @@ void CodeGenerator::AssembleMove(InstructionOperand* source,
         case Constant::kHeapObject:
           __ Move(dst, src.ToHeapObject());
           break;
+        case Constant::kRpoNumber:
+          UNREACHABLE();  // TODO(dcarney): loading RPO constants on arm.
+          break;
       }
       if (destination->IsStackSlot()) __ str(dst, g.ToMemOperand(destination));
     } else if (src.type() == Constant::kFloat32) {