[ARM][KFCI] Fix unused variable for llvm#163698

Author: googlewalt

llvm/lib/Target/ARM/ARMAsmPrinter.cpp

@@ -1640,7 +1640,9 @@ void ARMAsmPrinter::EmitKCFI_CHECK_Thumb2(Register AddrReg, int64_t Type,
     bool isLast = (i == 3);
 
     // Verify the immediate can be encoded as Thumb2 modified immediate.
+#ifndef NDEBUG
     int T2SOImmVal = ARM_AM::getT2SOImmVal(imm);
+#endif // NDEBUG
     assert(T2SOImmVal != -1 &&
            "Cannot encode immediate as Thumb2 modified immediate");