Subzero: Prototype to make use of RegNumT::No Register more concise

src/IceTargetLoweringX8664Traits.h

Index: src/IceTargetLoweringX8664Traits.h
diff --git a/src/IceTargetLoweringX8664Traits.h b/src/IceTargetLoweringX8664Traits.h
index 18e054ab9d295f1f376e1696247376c8a560a1b5..394fbb5e9e995711c8432e9b99815c815968dc8e 100644
--- a/src/IceTargetLoweringX8664Traits.h
+++ b/src/IceTargetLoweringX8664Traits.h
@@ -401,7 +401,7 @@ private:
 
 public:
   static RegNumT getGprForType(Type Ty, RegNumT RegNum) {
-    assert(RegNum != RegNumT::NoRegister);
+    assert(RegNum.hasValue());
 
     if (!isScalarIntegerType(Ty)) {
       return RegNum;