[ARM64] Fix lifting of mrs xzr, ... to not reference the xzr register

ARM64 lifting replaces references to the zero register with constant
zeroes. The zero register is not intended to appear in any lifted IL.

In the case of the `mrs` instruction, the destination being a zero
register means the system register is accessed only for a side-effect,
and is not stored anywhere. The lifting is updated to specify no output
registers for the intrinsic in that case.

Author: bdash

arch/arm64/il.cpp

@@ -2803,8 +2803,13 @@ bool GetLowLevelILForInstruction(
 				operand2.implspec[3], operand2.implspec[4]);
 		}
 
-		il.AddInstruction(
-		    il.Intrinsic({RegisterOrFlag::Register(REG_O(operand1))}, ARM64_INTRIN_MRS, {il.Const(4, reg)}));
+		if (IS_ZERO_REG(REG_O(operand1))) {
+			il.AddInstruction(
+			    il.Intrinsic({}, ARM64_INTRIN_MRS, {il.Const(4, reg)}));
+		} else {
+			il.AddInstruction(
+			    il.Intrinsic({RegisterOrFlag::Register(REG_O(operand1))}, ARM64_INTRIN_MRS, {il.Const(4, reg)}));
+		}
 		break;
 	}
 	case ARM64_MSUB: