Add basic support for folding hwintrinsic trees in morph

Author: tannergooding

src/coreclr/jit/compiler.h

@@ -3646,6 +3646,10 @@ class Compiler
     GenTree* gtFoldTypeCompare(GenTree* tree);
     GenTree* gtFoldTypeEqualityCall(bool isEq, GenTree* op1, GenTree* op2);
 
+#if defined(FEATURE_HW_INTRINSICS)
+    GenTree* gtFoldExprHWIntrinsic(GenTreeHWIntrinsic* tree);
+#endif // FEATURE_HW_INTRINSICS
+
     // Options to control behavior of gtTryRemoveBoxUpstreamEffects
     enum BoxRemovalOptions
     {