silence compiler warning

src/KOKKOS/pair_reaxff_kokkos.cpp

@@ -3238,7 +3238,9 @@ void PairReaxFFKokkos<DeviceType>::operator()(TagPairReaxComputeTorsionPreproces
   const F_FLOAT inv_sin_ijk_rnd = 1.0 / sin_ijk_rnd;
   const F_FLOAT inv_sin_jil_rnd = 1.0 / sin_jil_rnd;
 
-  #pragma unroll
+#ifdef LMP_KOKKOS_GPU
+#pragma unroll
+#endif
   for (int d = 0; d < 3; d++) {
     // dcos_omega_di
     F_FLOAT dcos_omega_dk = ((htra-arg*hnra) * inv_rik) * delik[d] - dellk[d];